Transcriber’s Notes


In this Plain Text version of this eBook, italics are enclosed within
~tildas~, superscripts and subscripts are enclosed in curly braces and
preceded by a caret ^{superscript} or an underscore _{subscript}.

Other notes will be found at the end of this eBook.




                 SMITHSONIAN MISCELLANEOUS COLLECTIONS
                          VOLUME 76, NUMBER 2


                       HISTORY OF ELECTRIC LIGHT


                                   BY
                            HENRY SCHROEDER
                          Harrison, New Jersey

                    [Illustration: FOR THE INCREASE
                            AND DIFFVSION OF
                          KNOWLEDGE AMONG MEN

                              SMITHSONIAN
                              INSTITVTION
                            WASHINGTON 1846]

                           (PUBLICATION 2717)


                           CITY OF WASHINGTON
                PUBLISHED BY THE SMITHSONIAN INSTITUTION
                            AUGUST 15, 1923




                        The Lord Baltimore Press
                        BALTIMORE, MD., U. S. A.




CONTENTS


                                                                    PAGE

  List of Illustrations                                                v

  Foreword                                                            ix

  Chronology of Electric Light                                        xi

  Early Records of Electricity and Magnetism                           1

  Machines Generating Electricity by Friction                          2

  The Leyden Jar                                                       3

  Electricity Generated by Chemical Means                              3

  Improvement of Volta’s Battery                                       5

  Davy’s Discoveries                                                   5

  Researches of Oersted, Ampère, Schweigger and Sturgeon               6

  Ohm’s Law                                                            7

  Invention of the Dynamo                                              7

  Daniell’s Battery                                                   10

  Grove’s Battery                                                     11

  Grove’s Demonstration of Incandescent Lighting                      12

  Grenet Battery                                                      13

  De Moleyns’ Incandescent Lamp                                       13

  Early Developments of the Arc Lamp                                  14

  Joule’s Law                                                         16

  Starr’s Incandescent Lamp                                           17

  Other Early Incandescent Lamps                                      19

  Further Arc Lamp Developments                                       20

  Development of the Dynamo, 1840–1860                                24

  The First Commercial Installation of an Electric Light              25

  Further Dynamo Developments                                         27

  Russian Incandescent Lamp Inventors                                 30

  The Jablochkoff “Candle”                                            31

  Commercial Introduction of the Differentially Controlled Arc Lamp   33

  Arc Lighting in the United States                                   33

  Other American Arc Light Systems                                    40

  “Sub-Dividing the Electric Light”                                   42

  Edison’s Invention of a Practical Incandescent Lamp                 43

  Edison’s Three-Wire System                                          53

  Development of the Alternating Current Constant Potential System    54

  Incandescent Lamp Developments, 1884–1894                           56

  The Edison “Municipal” Street Lighting System                       62

  The Shunt Box System for Series Incandescent Lamps                  64

  The Enclosed Arc Lamp                                               65

  The Flame Arc Lamp                                                  67

  The Constant Current Transformer for Series Circuits                69

  Enclosed Series Alternating Current Arc Lamps                       69

  Series Incandescent Lamps on Constant Current Transformers          70

  The Nernst Lamp                                                     71

  The Cooper-Hewitt Lamp                                              72

  The Luminous or Magnetite Arc Lamp                                  74

  Mercury Arc Rectifier for Magnetite Arc Lamps                       77

  Incandescent Lamp Developments, 1894–1904                           78

  The Moore Tube Light                                                79

  The Osmium Lamp                                                     82

  The Gem Lamp                                                        82

  The Tantalum Lamp                                                   84

  Invention of the Tungsten Lamp                                      85

  Drawn Tungsten Wire                                                 87

  The Quartz Mercury Vapor Arc Lamp                                   88

  The Gas-Filled Tungsten Lamp                                        89

  Types and Sizes of Tungsten Lamps Now Made                          91

  Standard Voltages                                                   93

  Cost of Incandescent Electric Light                                 93

  Statistics Regarding the Present Demand for Lamps                   94

  Selected Bibliography                                               95




LIST OF ILLUSTRATIONS


                                                                    PAGE

  Portion of the Electrical Exhibit in the United States National
      Museum                                                        viii

  Otto Von Guericke’s Electric Machine, 1650                           2

  Voltaic Pile, 1799                                                   4

  Faraday’s Dynamo, 1831                                               8

  Pixii’s Dynamo, 1832                                                 9

  Daniell’s Cell, 1836                                                10

  Grove’s Cell, 1838                                                  11

  Grove’s Incandescent Lamp, 1840                                     13

  De Moleyns’ Incandescent Lamp, 1841                                 14

  Wright’s Arc Lamp, 1845                                             15

  Archereau’s Arc Lamp, 1848                                          16

  Starr’s Incandescent Lamp, 1845                                     18

  Staite’s Incandescent Lamp, 1848                                    19

  Roberts’ Incandescent Lamp, 1852                                    19

  Farmer’s Incandescent Lamp, 1859                                    20

  Roberts’ Arc Lamp, 1852                                             21

  Slater and Watson’s Arc Lamp, 1852                                  21

  Diagram of “Differential” Method of Control of an Arc Lamp          22

  Lacassagne and Thiers’ Differentially Controlled Arc Lamp, 1856     23

  Serrin’s Arc Lamp, 1857                                             24

  Siemens’ Dynamo, 1856                                               25

  Alliance Dynamo, 1862                                               26

  Wheatstone’s Self-Excited Dynamo, 1866                              27

  Gramme’s Dynamo, 1871                                               28

  Gramme’s “Ring” Armature                                            28

  Alteneck’s Dynamo with “Drum” Wound Armature, 1872                  29

  Lodyguine’s Incandescent Lamp, 1872                                 30

  Konn’s Incandescent Lamp, 1875                                      30

  Bouliguine’s Incandescent Lamp, 1876                                31

  Jablochkoff “Candle,” 1876                                          32

  Jablochkoff’s Alternating Current Dynamo, 1876                      33

  Wallace-Farmer Arc Lamp, 1875                                       34

  Wallace-Farmer Dynamo, 1875                                         34

  Weston’s Arc Lamp, 1876                                             35

  Brush’s Dynamo, 1877                                                36

  Diagram of Brush Armature                                           36

  Brush’s Arc Lamp, 1877                                              37

  Thomson-Houston Arc Dynamo, 1878                                    38

  Diagram of T-H Arc Lighting System                                  39

  Thomson-Houston Arc Lamp, 1878                                      40

  Thomson Double Carbon Arc Lamp                                      40

  Maxim Dynamo                                                        41

  Sawyer’s Incandescent Lamp, 1878                                    42

  Farmer’s Incandescent Lamp, 1878                                    42

  Maxim’s Incandescent Lamp, 1878                                     43

  Edison’s First Experimental Lamp, 1878                              44

  Diagram of Constant Current Series System                           45

  Diagram of Edison’s Multiple System, 1879                           45

  Edison Dynamo, 1879                                                 46

  Edison’s High Resistance Platinum Lamp, 1879                        47

  Edison’s High Resistance Platinum in Vacuum Lamp, 1879              47

  Edison’s Carbon Lamp of October 21, 1879                            48

  Demonstration of Edison’s Incandescent Lighting System              49

  Dynamo Room, S. S. Columbia                                         50

  Original Socket for Incandescent Lamps                              51

  Wire Terminal Base Lamp, 1880                                       51

  Original Screw Base Lamp, 1880                                      52

  Improved Screw Base Lamp, 1881                                      52

  Final Form of Screw Base, 1881                                      53

  Diagram of Edison’s Three Wire System, 1881                         54

  Diagram of Stanley’s Alternating Current Multiple System, 1885      55

  Standard Edison Lamp, 1884                                          56

  Standard Edison Lamp, 1888                                          56

  Standard Edison Lamp, 1894                                          57

  Various Bases in Use, 1892                                          58

  Thomson-Houston Socket                                              59

  Westinghouse Socket                                                 59

  Adapters for Edison Screw Sockets, 1892                             60

  Various Series Bases in Use, 1892                                   61

  Edison “Municipal” System, 1885                                     62

  Edison “Municipal” Lamp, 1885                                       63

  Shunt Box System, 1887                                              64

  Enclosed Arc Lamp, 1893                                             65

  Open Flame Arc Lamp, 1898                                           66

  Enclosed Flame Arc Lamp, 1908                                       66

  Constant Current Transformer, 1900                                  68

  Series Incandescent Lamp Socket with Film Cutout, 1900              70

  Nernst Lamp, 1900                                                   71

  Diagram of Nernst Lamp                                              72

  Cooper-Hewitt Mercury Vapor Arc Lamp, 1901                          73

  Diagram of Cooper-Hewitt Lamp for Use on Alternating Current        74

  Luminous or Magnetite Arc Lamp, 1902                                75

  Diagram of Series Magnetite Arc Lamp                                76

  Mercury Arc Rectifier Tube for Series Magnetite Arc Circuits, 1902  77

  Early Mercury Arc Rectifier Installation                            78

  The Moore Tube Light, 1904                                          79

  Diagram of Feeder Valve of Moore Tube                               80

  Osmium Lamp, 1905                                                   82

  Gem Lamp, 1905                                                      83

  Tantalum Lamp, 1906                                                 84

  Tungsten Lamp, 1907                                                 86

  Drawn Tungsten Wire Lamp, 1911                                      87

  Quartz Mercury Vapor Lamp, 1912                                     88

  Gas Filled Tungsten Lamp, 1913                                      89

  Gas Filled Tungsten Lamp, 1923                                      90

  Standard Tungsten Lamps, 1923                                       92


[Illustration: PORTION OF THE ELECTRICAL EXHIBIT IN THE UNITED STATES
NATIONAL MUSEUM.

Section devoted to the historical development of the electric light and
dynamo.]




FOREWORD


In the year 1884 a Section of Transportation was organized in the
United States National Museum for the purpose of preparing and
assembling educational exhibits of a few objects of railroad machinery
which had been obtained both from the Centennial Exhibition held in
Philadelphia in 1876 and still earlier as incidentals to ethnological
collections, and to secure other collections relating to the railway
industry.

From this beginning the section was expanded to include the whole
field of engineering and is designated at present as the Divisions of
Mineral and Mechanical Technology. The growth and enlargement of the
collections has been particularly marked in the fields of mining and
mineral industries; mechanical engineering, especially pertaining to
the steam engine, internal combustion engine and locomotive; naval
architecture, and electrical engineering, particularly the development
of the telegraph, telephone and the electric light.

In the acquisition of objects visualizing the history of electric
light the Museum has been rather fortunate, particularly as regards
the developments in the United States. Thus mention may be made of
the original Patent Office models of the more important dynamos, arc
lights and incandescent lights, together with original commercial
apparatus after these models; a unit of the equipment used in the
first commercially successful installation on land of an incandescent
lighting system, presented by Joseph E. Hinds in whose engraving
establishment in New York City the installation was made in 1881; and
a large series of incandescent lights, mainly originals, visualizing
chronologically the developments of the Edison light from its
inception, presented at intervals since the year 1898 by the General
Electric Company.

The object of all collections in the Divisions is to visualize
broadly the steps by which advances have been made in each field of
engineering; to show the layman the fundamental and general principles
which are the basis for the developments; and to familiarize the
engineer with branches of engineering other than his own. Normally
when a subject is completely covered by a collection of objects, a
paper is prepared and published describing the collection and the
story it portrays. In the present instance, however, on account of
the uncertainty of the time of completing the collection, if it is
possible ever to bring this about, it was thought advisable to publish
Mr. Schroeder’s paper which draws upon the Museum collection as
completely as possible.

                                  CARL W. MITMAN,
                                      ~Curator, Divisions of Mineral and
                                          Mechanical Technology,
                                              U. S. National Museum~.




CHRONOLOGY OF ELECTRIC LIGHT


  1800--Allesandro Volta demonstrated his discovery that electricity
          can be generated by chemical means. The VOLT, the unit of
          electric pressure, is named in his honor for this discovery
          of the electric battery.

  1802--Sir Humphry Davy demonstrated that electric current can heat
          carbon and strips of metal to incandescence and give light.

  1809--Sir Humphry Davy demonstrated that current will give a
          brilliant flame between the ends of two carbon pencils
          which are first allowed to touch each other and then pulled
          apart. This light he called the “arc” on account of its
          arch shape.

  1820--André Marie Ampère discovered that current flowing through
          a coiled wire gives it the properties of a magnet. The
          AMPERE, the unit of flow of electric current, is named in
          his honor for this discovery.

  1825--Georg Simon Ohm discovered the relation between the voltage,
          ampereage and resistance in an electric circuit, which is
          called Ohm’s Law. The OHM, the unit of electric resistance,
          is named in his honor for this discovery.

  1831--Michael Faraday discovered that electricity can be generated
          by moving a wire in the neighborhood of a magnet, the
          principle of the dynamo.

  1840--Sir William Robert Grove demonstrated his experimental
          incandescent lamp in which platinum is made incandescent by
          current flowing through it.

  1841--Frederick De Moleyns obtained the first patent on an
          incandescent lamp. The burner was powdered charcoal
          operating in an exhausted glass globe.

  1845--Thomas Wright obtained the first patent on an arc light.

  1845--J. W. Starr invented an incandescent lamp consisting of a
          carbon pencil operating in the vacuum above a column of
          mercury.

  1856--Joseph Lacassagne and Henry Thiers invented the
          “differential” method of control of the arc which was
          universally used twenty years later when the arc lamp was
          commercially established.

  1862--The first commercial installation of an electric light. An
          arc light was put in a lighthouse in England.

  1866--Sir Charles Wheatstone invented the “self-excited” dynamo,
          now universally used.

  1872--Lodyguine invented an incandescent lamp having a graphite
          burner operating in nitrogen gas.

  1876--Paul Jablochkoff invented the “electric candle,” an arc light
          commercially used for lighting the boulevards in Paris.

  1877–8--Arc light systems commercially established in the United
          States by William Wallace and Prof. Moses Farmer, Edward
          Weston, Charles F. Brush and Prof. Elihu Thomson and Edwin
          J. Houston.

  1879--Thomas Alva Edison invented an incandescent lamp consisting
          of a high resistance carbon filament operating in a
          high vacuum maintained by an all glass globe. These
          principles are used in all incandescent lamps made today.
          He also invented a completely new system of distributing
          electricity at constant pressure, now universally used.

  1882--Lucien Goulard and John D. Gibbs invented a series
          alternating current system of distributing electric
          current. This has not been commercially used.

  1886--William Stanley invented a constant pressure alternating
          current system of distribution. This is universally used
          where current is to be distributed long distances.

  1893--Louis B. Marks invented the enclosed carbon arc lamp.

  1898--Bremer’s invention of the flame arc lamp, having carbons
          impregnated with various salts, commercially established.

  1900--Dr. Walther Nernst’s invention of the Nernst lamp
          commercially established. The burner consisted of various
          oxides, such as zirconia, which operated in the open air.

  1901--Dr. Peter Cooper Hewitt’s invention of the mercury arc light
          commercially established.

  1902--The magnetite arc lamp was developed by C. A. B. Halvorson,
          Jr. This has a new method of control of the arc. The
          negative electrode consists of a mixture of magnetite and
          other substances packed in an iron tube.

  1904--D. McFarlan Moore’s invention of the Moore vacuum tube light
          commercially established. This consisted of a long tube,
          made in lengths up to 200 feet, from which the air had been
          exhausted to about a thousandth of an atmosphere. High
          voltage current passing through this rarefied atmosphere
          caused it to glow. Rarefied carbon dioxide gas was later
          used.

  1905--Dr. Auer von Welsbach’s invention of the osmium incandescent
          lamp commercially established, but only on a small scale
          in Europe. The metal osmium, used for the filament which
          operated in vacuum, is rarer and more expensive than
          platinum.

  1905--Dr. Willis R. Whitney’s invention of the Gem incandescent
          lamp commercially established. The carbon filament had been
          heated to a very high temperature in an electric resistance
          furnace invented by him. The lamp was 25 per cent more
          efficient than the regular carbon lamp.

  1906--Dr. Werner von Bolton’s invention of the tantalum
          incandescent lamp commercially established.

  1907--Alexander Just and Franz Hanaman’s invention of the tungsten
          filament incandescent lamp commercially established.

  1911--Dr. William D. Coolidge’s invention of drawn tungsten wire
          commercially established.

  1913--Dr. Irving Langmuir’s invention of the gas-filled tungsten
          filament incandescent lamp commercially established.




                       HISTORY OF ELECTRIC LIGHT

                          BY HENRY SCHROEDER,
                         HARRISON, NEW JERSEY.




EARLY RECORDS OF ELECTRICITY AND MAGNETISM


About twenty-five centuries ago, Thales, a Greek philosopher, recorded
the fact that if amber is rubbed it will attract light objects.
The Greeks called amber “elektron,” from which we get the word
“electricity.” About two hundred and fifty years later, Aristotle,
another Greek philosopher, mentioned that the lodestone would attract
iron. Lodestone is an iron ore (Fe_{3}O_{4}), having magnetic qualities
and is now called magnetite. The word “magnet” comes from the fact that
the best specimens of lodestones came from Magnesia, a city in Asia
Minor. Plutarch, a Greek biographer, wrote about 100 A. D., that iron
is sometimes attracted and at other times repelled by a lodestone. This
indicates that the piece of iron was magnetised by the lodestone.

In 1180, Alexander Neckham, an English Monk, described the compass,
which probably had been invented by sailors of the northern countries
of Europe, although its invention has been credited to the Chinese.
Early compasses probably consisted of an iron needle, magnetised by
a lodestone, mounted on a piece of wood floating in water. The word
lodestone or “leading stone” comes from the fact that it would point
towards the north if suspended like a compass.

William Gilbert, physician to Queen Elizabeth of England, wrote a
book about the year 1600 giving all the information then known on
the subject. He also described his experiments, showing, among other
things, the existence of magnetic lines of force and of north and south
poles in a magnet. Robert Norman had discovered a few years previously
that a compass needle mounted on a horizontal axis would dip downward.
Gilbert cut a large lodestone into a sphere, and observed that the
needle did not dip at the equator of this sphere, the dip increasing
to 90 degrees as the poles were approached. From this he deduced that
the earth was a magnet with the magnetic north pole at the geographic
north pole. It has since been determined that these two poles do not
coincide. Gilbert suggested the use of the dipping needle to determine
latitude. He also discovered that other substances, beside amber, would
attract light objects if rubbed.




MACHINES GENERATING ELECTRICITY BY FRICTION


Otto Von Guericke was mayor of the city of Magdeburg as well as a
philosopher. About 1650 he made a machine consisting of a ball of
sulphur mounted on a shaft which could be rotated. Electricity was
generated when the hand was pressed against the globe as it rotated.
He also discovered that electricity could be conducted away from the
globe by a chain and would appear at the other end of the chain. Von
Guericke also invented the vacuum air pump. In 1709, Francis Hawksbee,
an Englishman, made a similar machine, using a hollow glass globe which
could be exhausted. The exhausted globe when rotated at high speed and
rubbed by hand would produce a glowing light. This “electric light” as
it was called, created great excitement when it was shown before the
Royal Society, a gathering of scientists, in London.

[Illustration: OTTO VON GUERICKE’S ELECTRIC MACHINE, 1650.

A ball of sulphur was rotated, electricity being generated when it
rubbed against the hand.]

Stephen Gray, twenty years later, showed the Royal Society that
electricity could be conducted about a thousand feet by a hemp thread,
supported by silk threads. If metal supports were used, this could not
be done. Charles du Fay, a Frenchman, repeated Gray’s experiments,
and showed in 1733 that the substances which were insulators, and
which Gilbert had discovered, would become electrified if rubbed.
Those substances which Gilbert could not electrify were conductors of
electricity.




THE LEYDEN JAR


The thought came to Von Kleist, Bishop of Pomerania, Germany, about
1745, that electricity could be stored. The frictional machines
generated so small an amount of electricity (though, as is now known,
at a very high pressure--several thousand volts) that he thought he
could increase the quantity by storing it. Knowing that glass was
an insulator and water a conductor, he filled a glass bottle partly
full of water with a nail in the cork to connect the machine with the
water. Holding the bottle in one hand and turning the machine with
the other for a few minutes, he then disconnected the bottle from the
machine. When he touched the nail with his other hand he received a
shock which nearly stunned him. This was called the Leyden jar, the
forerunner of the present condenser. It received its name from the fact
that its discovery was also made a short time after by experimenters
in the University of Leyden. Further experiments showed that the hand
holding the bottle was as essential as the water inside, so these were
substituted by tin foil coatings inside and outside the bottle.

Benjamin Franklin, American statesman, scientist and printer, made
numerous experiments with the Leyden jar. He connected several jars
in parallel, as he called it, which gave a discharge strong enough to
kill a turkey. He also connected the jars in series, or “in cascade” as
he called it, thus establishing the principle of parallel and series
connections. Noticing the similarity between the electric spark and
lightning, Franklin in 1752, performed his famous kite experiment.
Flying a kite in a thunderstorm, he drew electricity from the clouds to
charge Leyden jars, which were later discharged, proving that lightning
and electricity were the same. This led him to invent the lightning rod.




ELECTRICITY GENERATED BY CHEMICAL MEANS


Luigi Galvani was an Italian scientist. About 1785, so the story goes,
his wife was in delicate health, and some frog legs were being skinned
to make her a nourishing soup. An assistant holding the legs with a
metal clamp and cutting the skin with a scalpel, happened to let the
clamp and scalpel touch each other. To his amazement the frog legs
twitched. Galvani repeated the experiment many times by touching
the nerve with a metal rod and the muscle with a different metal rod
and allowing the rods to touch, and propounded the theory of animal
electricity in a paper he published in 1791.

Allesandro Volta, a professor of physics in the University of Pavia,
Italy, read about Galvani’s work and repeated his experiments. He
found that the extent of the movement of the frog legs depended on the
metals used for the rods, and thus believed that the electric charge
was produced by the contact of dissimilar metals with the moisture in
the muscles. To prove his point he made a pile of silver and zinc discs
with cloths, wet with salt water, between them. This was in 1799, and
he described his pile in March, 1800, in a letter to the Royal Society
in London.

[Illustration: VOLTAIC PILE, 1799.

Volta discovered that electricity could be generated by chemical means
and made a pile of silver and zinc discs with cloths, wet with salt
water, between them. This was the forerunner of the present-day dry
battery. Photograph courtesy Prof. Chas. F. Chandler Museum, Columbia
University, New York.]

This was an epoch-making discovery as it was the forerunner of the
present-day primary battery. Volta soon found that the generation of
electricity became weaker as the cloths became dry, so to overcome
this he made his “crown of cups.” This consisted of a series of cups
containing salt water in which strips of silver and zinc were dipped.
Each strip of silver in one cup was connected to the zinc strip in
the next cup, the end strips of silver and zinc being terminals of
the battery. This was the first time that a continuous supply of
electricity in reasonable quantities was made available, so the VOLT,
the unit of electrical pressure was named in his honor. It was later
shown that the chemical affinity of one of the metals in the liquid was
converted into electric energy. The chemical action of Volta’s battery
is that the salt water attacks the zinc when the circuit is closed
forming zinc chloride, caustic soda and hydrogen gas. The chemical
equation is:

            Zn + 2NaCl + 2H_{2}O = ZnCl_{2} + 2NaOH + H_{2}




IMPROVEMENT OF VOLTA’S BATTERY


It was early suggested that sheets of silver and zinc be soldered
together back to back and that a trough be divided into cells by these
bimetal sheets being put into grooves cut in the sides and bottom of
the trough. This is the reason why one unit of a battery is called a
“cell.” It was soon found that a more powerful cell could be made if
copper, zinc and dilute sulphuric acid were used. The zinc is dissolved
by the acid forming zinc sulphate and hydrogen gas, thus:

                  Zn + H_{2}SO_{4} = ZnSO_{4} + H_{2}

The hydrogen gas appears as bubbles on the copper and reduces the open
circuit voltage (about 0.8 volt per cell) as current is taken from the
battery. This is called “polarization.” Owing to minute impurities in
the zinc, it is attacked by the acid even when no current is taken from
the battery, the impurities forming with the zinc a short circuited
local cell. This is called “local action,” and this difficulty was at
first overcome by removing the zinc from the acid when the battery was
not in use.




DAVY’S DISCOVERIES


Sir Humphry Davy was a well-known English chemist, and with the aid of
powerful batteries constructed for the Royal Institution in London,
he made numerous experiments on the chemical effects of electricity.
He decomposed a number of substances and discovered the elements
boron, potassium and sodium. He heated strips of various metals to
incandescence by passing current through them, and showed that platinum
would stay incandescent for some time without oxidizing. This was about
1802.

In the early frictional machines, the presence of electricity was shown
by the fact that sparks could be obtained. Similarly the breaking
of the circuit of a battery would give a spark. Davy, about 1809,
demonstrated that this spark could be maintained for a long time with
the large battery of 2000 cells he had had constructed. Using two
sticks of charcoal connected by wires to the terminals of this very
powerful battery, he demonstrated before the Royal Society the light
produced by touching the sticks together and then holding them apart
horizontally about three inches. The brilliant flame obtained he called
an “arc” because of its arch shape, the heated gases, rising, assuming
this form. Davy was given the degree of LL. D. for his distinguished
research work, and was knighted on the eve of his marriage, April 11,
1812.




RESEARCHES OF OERSTED, AMPÈRE, SCHWEIGGER AND STURGEON


Hans Christian Oersted was a professor of physics at the University of
Copenhagen in Denmark. One day in 1819, while addressing his students,
he happened to hold a wire, through which current was flowing, over
a large compass. To his surprise he saw the compass was deflected
from its true position. He promptly made a number of experiments and
discovered that by reversing the current the compass was deflected in
the opposite direction. Oersted announced his discovery in 1820.

André Marie Ampère was a professor of mathematics in the Ecole
Polytechnic in Paris. Hearing of Oersted’s discovery, he immediately
made some experiments and made the further discovery in 1820 that if
the wire is coiled and current passed through it, the coil had all the
properties of a magnet.

These two discoveries led to the invention of Schweigger in 1820,
of the galvanometer (or “multiplier” as it was then called), a very
sensitive instrument for measuring electric currents. It consisted of
a delicate compass needle suspended in a coil of many turns of wire.
Current in the coil deflected the needle, the direction and amount of
deflection indicating the direction and strength of the current. Ampère
further made the discovery that currents in opposite directions repel
and in the same directions attract each other. He also gave a rule
for determining the direction of the current by the deflection of the
compass needle. He developed the theory that magnetism is caused by
electricity flowing around the circumference of the body magnetised.
The AMPERE, the unit of flow of electric current, was named in honor of
his discoveries.

In 1825 it was shown by Sturgeon that if a bar of iron were placed in
the coil, its magnetic strength would be very greatly increased, which
he called an electro-magnet.




OHM’S LAW


Georg Simon Ohm was born in Bavaria, the oldest son of a poor
blacksmith. With the aid of friends he went to college and became a
teacher. It had been shown that the rate of transfer of heat from one
end to the other of a metal bar is proportional to the difference
of temperature between the ends. About 1825, Ohm, by analogy and
experiment, found that the current in a conductor is proportional to
the difference of electric pressure (voltage) between its ends. He
further showed that with a given difference of voltage, the current
in different conductors is inversely proportional to the resistance
of the conductor. Ohm therefore propounded the law that the current
flowing in a circuit is equal to the voltage on that circuit divided by
the resistance of the circuit. In honor of this discovery, the unit of
electrical resistance is called the OHM. This law is usually expressed
as:

                                C = E/R

“C” meaning current (in amperes), “E” meaning electromotive force or
voltage (in volts) and “R” meaning resistance (in ohms).

This is one of the fundamental laws of electricity and if thoroughly
understood, will solve many electrical problems. Thus, if any two of
the above units are known, the third can be determined. Examples: An
incandescent lamp on a 120-volt circuit consumes 0.4 ampere, hence its
resistance under such conditions is 300 ohms. Several trolley cars at
the end of a line take 100 amperes to run them and the resistance of
the overhead wire from the power house to the trolley cars is half
an ohm; the drop in voltage on the line between the power house and
trolley cars is therefore 50 volts, so that if the voltage at the power
house were 600, it would be 550 volts at the end of the line.

Critics derided Ohm’s law so that he was forced out of his position
as teacher in the High School in Cologne. Finally after ten years Ohm
began to find supporters and in 1841 his law was publicly recognized by
the Royal Society of London which presented him with the Copley medal.




INVENTION OF THE DYNAMO


Michael Faraday was an English scientist. Born of parents in poor
circumstances, he became a bookbinder and studied books on electricity
and chemistry. He finally obtained a position as laboratory assistant
to Sir Humphry Davy helping him with his lectures and experiments. He
also made a number of experiments himself and succeeded in liquifying
chlorine gas for which he was elected to a Fellowship in the Royal
Institution in 1824. Following up Oersted’s and Ampère’s work, he
endeavored to find the relation between electricity and magnetism.
Finally on Oct. 17, 1831, he made the experiment of moving a permanent
bar magnet in and out of a coil of wire connected to a galvanometer.
This generated electricity in the coil which deflected the galvanometer
needle. A few days after, Oct. 28, 1831, he mounted a copper disk
on a shaft so that the disk could be rotated between the poles of
a permanent horseshoe magnet. The shaft and edge of the disk were
connected by brushes and wires to a galvanometer, the needle of which
was deflected as the disk was rotated. A paper on his invention was
read before the Royal Society on November 24, 1831, which appeared in
printed form in January, 1832.

[Illustration: FARADAY’S DYNAMO, 1831.

Faraday discovered that electricity could be generated by means of a
permanent magnet. This principle is used in all dynamos.]

Faraday did not develop his invention any further, being satisfied,
as in all his work, in pure research. His was a notable invention but
it remained for others to make it practicable. Hippolyte Pixii, a
Frenchman, made a dynamo in 1832 consisting of a permanent horseshoe
magnet which could be rotated between two wire bobbins mounted on a
soft iron core. The wires from the bobbins were connected to a pair of
brushes touching a commutator mounted on the shaft holding the magnet,
and other brushes carried the current from the commutator so that the
alternating current generated was rectified into direct current.

[Illustration: PIXII’S DYNAMO, 1832.

Pixii made an improvement by rotating a permanent magnet in the
neighborhood of coils of wire mounted on a soft iron core. A commutator
rectified the alternating current generated into direct current. This
dynamo is in the collection of the Smithsonian Institution.]

E. M. Clarke, an Englishman made, in 1834, another dynamo in which the
bobbins rotated alongside of the poles of a permanent horseshoe magnet.
He also made a commutator so that the machine produced direct current.
None of these machines gave more than feeble current at low pressure.
The large primary batteries that had been made were much more powerful,
although expensive to operate. It has been estimated that the cost of
current from the 2000-cell battery to operate the demonstration of the
arc light by Davy, was six dollars a minute. At present retail rates
for electricity sold by lighting companies, six dollars would operate
Davy’s arc light about 500 hours or 30,000 times as long.




DANIELL’S BATTERY


[Illustration: DANIELL’S CELL, 1836.

Daniell invented a battery consisting of zinc, copper and copper
sulphate. Later the porous cup was dispensed with, which was used to
keep the sulphuric acid formed separate from the solution of copper
sulphate, the two liquids then being kept apart by their difference in
specific gravity. It was then called the Gravity Battery and for years
was used in telegraphy.]

It was soon discovered that if the zinc electrode were rubbed with
mercury (amalgamated), the local action would practically cease, and if
the hydrogen bubbles were removed, the operating voltage of the cell
would be increased. John Frederic Daniell, an English chemist, invented
a cell in 1836 to overcome these difficulties. His cell consisted
of a glass jar containing a saturated solution of copper sulphate
(CuSO_{4}). A copper cylinder, open at both ends and perforated with
holes, was put into this solution. On the outside of the copper
cylinder there was a copper ring, located below the surface of the
solution, acting as a shelf to support crystals of copper sulphate.
Inside the cylinder there was a porous earthenware jar containing
dilute sulphuric acid and an amalgamated zinc rod. The two liquids were
therefore kept apart but in contact with each other through the pores
of the jar. The hydrogen gas given off by the action of the sulphuric
acid on the zinc, combined with the dissolved copper sulphate, formed
sulphuric acid and metallic copper. The latter was deposited on the
copper cylinder which acted as the other electrode. Thus the copper
sulphate acted as a depolarizer.

The chemical reactions in this cell are,

        In inner porous jar: Zn + H_{2}SO_{4} = ZnSO_{4} + H_{2}
        In outer glass jar: H_{2} + CuSO_{4} = H_{2}SO_{4} + Cu

This cell had an open circuit voltage of a little over one volt. Later
the porous cup was dispensed with, the two liquids being kept apart
by the difference of their specific gravities. This was known as the
Gravity cell, and for years was used in telegraphy.

[Illustration: GROVE’S CELL, 1838.

This consisted of zinc, sulphuric acid, nitric acid and platinum. It
made a very powerful battery. The nitric acid is called the depolarizer
as it absorbs the hydrogen gas formed, thus improving the operating
voltage.]




GROVE’S BATTERY


Sir William Robert Grove, an English Judge and scientist, invented a
cell in 1838 consisting of a platinum electrode in strong nitric acid
in a porous earthenware jar. This jar was put in dilute sulphuric acid
in a glass jar in which there was an amalgamated zinc plate for the
other electrode. This had an open circuit voltage of about 1.9 volts.
The porous jar was used to prevent the nitric acid from attacking the
zinc. The nitric acid was used for the purpose of combining with the
hydrogen gas set free by the action of the sulphuric acid on the zinc,
and hence was the depolarizing agent. Hydrogen combining with nitric
acid forms nitrous peroxide and water. Part of the nitrous peroxide is
dissolved in the water, and the rest escapes as fumes which, however,
are very suffocating.

The chemical equations of this cell are as follows:

      In outer glass jar: Zn + H_{2}SO_{4} = ZnSO_{4} + H_{2}
      In inner porous jar: H_{2} + 2HNO_{3} = N_{2}O_{4} + 2H_{2}O

An interesting thing about Grove’s cell is that it was planned in
accordance with a theory. Grove knew that the electrical energy of
the zinc-sulphuric acid cell came from the chemical affinity of the
two reagents, and if the hydrogen gas set free could be combined with
oxygen (to form water--H_{2}O), such chemical affinity should increase
the strength of the cell. As the hydrogen gas appears at the other
electrode, the oxidizing agent should surround that electrode. Nitric
acid was known at that time as one of the most powerful oxidizing
liquids, but as it attacks copper, he used platinum for the other
electrode. Thus he not only overcame the difficulty of polarization by
the hydrogen gas, but also increased the voltage of the cell by the
added chemical action of the combination of hydrogen and oxygen.




GROVE’S DEMONSTRATION OF INCANDESCENT LIGHTING


In 1840 Grove made an experimental lamp by attaching the ends of a coil
of platinum wire to copper wires, the lower parts of which were well
varnished for insulation. The platinum wire was covered by a glass
tumbler, the open end set in a glass dish partly filled with water.
This prevented draughts of air from cooling the incandescent platinum,
and the small amount of oxygen of the air in the tumbler reduced the
amount of oxidization of the platinum that would otherwise occur. With
current supplied by a large number of cells of his battery, he lighted
the auditorium of the Royal Institution with these lamps during one
of the lectures he gave. This lamp gave only a feeble light as there
was danger of melting the platinum and platinum gives but little light
unless operated close to its melting temperature. It also required a
lot of current to operate it as the air tended to cool the incandescent
platinum. The demonstration was only of scientific interest, the cost
of current being much too great (estimated at several hundred dollars a
kilowatt hour) to make it commercial.




GRENET BATTERY


It was discovered that chromic anhydride gives up oxygen easier than
nitric acid and consequently if used would give a higher voltage than
Grove’s nitric acid battery. It also has the advantage of a lesser
tendency to attack zinc directly if it happens to come in contact with
it. Grenet developed a cell having a liquid consisting of a mixture of
potassium bichromate (K_{2}Cr_{2}O_{7}) and sulphuric acid. A porous
cell was therefore not used to keep the two liquids apart. This had the
advantage of reducing the internal resistance. The chemical reaction
was:

  K_{2}Cr_{2}O_{7} (potassium bichromate) + 7H_{2}SO_{4} (sulphuric
      acid) + 3Zn (zinc) = 3ZnSO_{4} (zinc sulphate) + K_{2}SO_{4}
      (potassium sulphate) + Cr_{2} (SO_{4})_{3} (chromium sulphate)
      + 7H_{2}O (water).

In order to prevent the useless consumption of zinc on open circuit,
the zinc was attached to a sliding rod and could be drawn up into the
neck of the bottle-shaped jar containing the liquid.

[Illustration: GROVE’S INCANDESCENT LAMP, 1840.

Grove made an experimental lamp, using platinum for the burner which
was protected from draughts of air by a glass tumbler.]




DE MOLEYNS’ INCANDESCENT LAMP


Frederick De Moleyns, an Englishman, has the honor of having obtained
the first patent on an incandescent lamp. This was in 1841 and his
lamp was quite novel. It consisted of a spherical glass globe, in the
upper part of which was a tube containing powdered charcoal. This tube
was open at the bottom inside the globe and through it ran a platinum
wire, the end below the tube being coiled. Another platinum wire coiled
at its upper end came up through the lower part of the globe but did
not quite touch the other platinum coil. The powdered charcoal filled
the two coils of platinum wire and bridged the gap between. Current
passing through this charcoal bridge heated it to incandescence. The
air in the globe having been removed as far as was possible with the
hand air pumps then available, the charcoal did not immediately burn
up, the small amount consumed being replaced by the supply in the
tube. The idea was ingenious but the lamp was impractical as the globe
rapidly blackened from the evaporation of the incandescent charcoal.

[Illustration: DE MOLEYNS’ INCANDESCENT LAMP, 1841.

This consisted of two coils of platinum wire containing powdered
charcoal operating in a vacuum. It is only of interest as the first
incandescent lamp on which a patent (British) was granted.]




EARLY DEVELOPMENTS OF THE ARC LAMP


It had been found that most of the light of the arc came from the
tip of the positive electrode, and that the charcoal electrodes were
rapidly consumed, the positive electrode about twice as fast as the
negative. Mechanisms were designed to take care of this, together with
devices to start the arc by allowing the electrodes to touch each other
and then pulling them apart the proper distance. This distance varied
from one-eighth to three-quarters of an inch.

In 1840 Bunsen, the German chemist who invented the bunsen burner,
devised a process for making hard dense carbon pencils which lasted
much longer than the charcoal previously used. The dense carbon from
the inside of the retorts of gas making plants was ground up and mixed
with molasses, moulded into shape and baked at a high temperature.
Bunsen also, in 1843, cheapened Grove’s battery by substituting a hard
carbon plate in place of the platinum electrode.

[Illustration: WRIGHT’S ARC LAMP, 1845.

This lamp is also only of interest as the first arc lamp on which a
patent (British) was granted. Four arcs played between the five carbon
discs.]

Thomas Wright, an Englishman, was the first to patent an arc lamp.
This was in 1845, and the lamp was a hand regulated device consisting
of five carbon disks normally touching each other and rotated by
clockwork. Two of the disks could be drawn outward by thumb screws,
which was to be done after the current was turned on thus establishing
four arcs, one between each pair of disks. The next year, 1846, W. E.
Staite, another Englishman, made an arc lamp having two vertical carbon
pencils. The upper was stationary. The lower was movable and actuated
by clockwork directed by ratchets which in turn were regulated by an
electro-magnet controlled by the current flowing through the arc. Thus
the lower carbon would be moved up or down as required.

Archereau, a Frenchman, made a very simple arc lamp in 1848. The upper
carbon was fixed and the lower one was mounted on a piece of iron
which could be drawn down into a coil of wire. The weight of the lower
electrode was overbalanced by a counterweight, so that when no current
was flowing the two carbons would touch. When current was turned on, it
flowed through the two carbons and through the coil of wire (solenoid)
which then became energized and pulled the lower carbon down, thus
striking the arc. Two of these arc lamps were installed in Paris
and caused considerable excitement. After a few weeks of unreliable
operation, it was found that the cost of current from the batteries was
much too great to continue their use commercially. The dynamo had not
progressed far enough to permit its use.

[Illustration: ARCHEREAU’S ARC LAMP, 1848.

This simple arc was controlled by an electro-magnet, and two lamps were
installed for street lighting in Paris, current being obtained from
batteries.]




JOULE’S LAW


Joule was an Englishman, and in 1842 began investigating the relation
between mechanical energy and heat. He first showed that, by allowing
a weight to drop from a considerable height and turn a paddle wheel in
water, the temperature of the water would increase in relation to the
work done in turning the wheel. It is now known that 778 foot-pounds
(1 lb. falling 778 feet, 10 lbs. falling 77.8 feet or 778 lbs. falling
one foot, etc.) is the mechanical equivalent of energy equal to raising
one pound of water one degree Fahrenheit. The rate of energy (power)
is the energy divided by a unit of time; thus one horsepower is 33,000
foot-pounds per minute. Joule next investigated the relation between
heat and electric current. He made a device consisting of a vessel of
water in which there were a thermometer and an insulated coil of wire
having a considerable resistance. He found that an electric current
heated the water, and making many combinations of the amount and length
of time of current flowing and of the resistance of the wire, he
deduced the law that the energy in an electric circuit is proportional
to the square of the amount of current flowing multiplied by the length
of time and multiplied by the resistance of the wire.

The rate of electrical energy (electric power) is therefore
proportional to the square of current multiplied by the resistance.
The electrical unit of power is now called the WATT, named in honor of
James Watt, the Englishman, who made great improvements to the steam
engine about a century ago. Thus, watts = C^{2}R and substituting the
value of R from Ohm’s law, C = E/R, we get

                        Watts = Volts × Amperes

The watt is a small unit of electric power, as can be seen from the
fact that 746 watts are equal to one horsepower. The kilowatt, kilo
being the Greek word for thousand, is 1000 watts.

This term is an important one in the electrical industry. For example,
dynamos are rated in kilowatts, expressed as KW; the largest one
made so far is 50,000 KW which is 66,666 horsepower. Edison’s first
commercial dynamo had a capacity of 6 KW although the terms watts
and kilowatts were not in use at that time. The ordinary sizes of
incandescent lamps now used in the home are 25, 40 and 50 watts.




STARR’S INCANDESCENT LAMP


[Illustration: STARR’S INCANDESCENT LAMP, 1845.

This consisted of a short carbon pencil operating in the vacuum above a
column of mercury.]

J. W. Starr, an American, of Cincinnati, Ohio, assisted financially by
Peabody, the philanthropist, went to England where he obtained a patent
in 1845 on the lamps he had invented, although the patent was taken
out under the name of King, his attorney. One is of passing interest
only. It consisted of a strip of platinum, the active length of which
could be adjusted to fit the battery strength used, and was covered
by a glass globe to protect it from draughts of air. The other, a
carbon lamp, was the first real contribution to the art. It consisted
of a rod of carbon operating in the vacuum above a column of mercury
(Torrecellium vacuum) as in a barometer. A heavy platinum wire was
sealed in the upper closed end of a large glass tube, and connected
to the carbon rod by an iron clamp. The lower end of the carbon rod
was fastened to another iron clamp, the two clamps being held in place
and insulated from each other by a porcelain rod. Attached to the
lower clamp was a long copper wire. Just below the lower clamp, the
glass tube was narrowed down and had a length of more than 30 inches.
The tube was then filled with mercury, the bottom of the tube being
put into a vessel partly full of mercury. The mercury ran out of the
enlarged upper part of the tube, coming to rest in the narrow part
of the tube as in a barometer, so that the carbon rod was then in a
vacuum. One lamp terminal was the platinum wire extending through the
top of the tube, and the other was the mercury. Several of these lamps
were put on exhibition in London, but were not a commercial success
as they blackened very rapidly. Starr started his return trip to the
United States the next year, but died on board the ship when he was but
25 years old.




OTHER EARLY INCANDESCENT LAMPS


[Illustration: STAITE’S INCANDESCENT LAMP, 1848.

The burner was of platinum and iridium.]

[Illustration: ROBERTS’ INCANDESCENT LAMP, 1852.

It had a graphite burner operating in vacuum.]

In 1848 W. E. Staite, who two years previously had made an arc lamp,
invented an incandescent lamp. This consisted of a platinum-iridium
burner in the shape of an inverted U, covered by a glass globe. It had
a thumb screw for a switch, the whole device being mounted on a bracket
which was used for the return wire. E. C. Shepard, another Englishman,
obtained a patent two years later on an incandescent lamp consisting of
a weighted hollow charcoal cylinder the end of which pressed against a
charcoal cone. Current passing through this high resistance contact,
heated the charcoal to incandescence. It operated in a glass globe from
which the air could be exhausted. M. J. Roberts obtained an English
patent in 1852 on an incandescent lamp. This had a graphite rod for a
burner, which could be renewed, mounted in a glass globe. The globe was
cemented to a metallic cap fastened to a piece of pipe through which
the air could be exhausted. After being exhausted, the pipe, having a
stop cock, could be screwed on a stand to support the lamp.

Moses G. Farmer, a professor at the Naval Training Station at Newport,
Rhode Island, lighted the parlor of his home at 11 Pearl Street, Salem,
Mass., during July, 1859, with several incandescent lamps having a
strip of platinum for the burner. The novel feature of this lamp was
that the platinum strip was narrower at the terminals than in the
center. Heat is conducted away from the terminals and by making the
burner thin at these points, the greater resistance of the ends of
the burner absorbed more electrical energy thus offsetting the heat
being conducted away. This made a more uniform degree of incandescence
throughout the length of the burner, and Prof. Farmer obtained a patent
on this principle many years later (1882).

[Illustration: FARMER’S INCANDESCENT LAMP, 1859.

This experimental platinum lamp was made by Professor Farmer and
several of them lighted the parlor of his home in Salem, Mass.]




FURTHER ARC LAMP DEVELOPMENTS


During the ten years, 1850 to 1860, several inventors developed arc
lamp mechanisms. Among them was M. J. Roberts, who had invented the
graphite incandescent lamp. In Roberts’ arc lamp, which he patented in
1852, the lower carbon was stationary. The upper carbon fitted snugly
into an iron tube. In the tube was a brass covered iron rod, which
by its weight could push the upper carbon down the tube so the two
carbons normally were in contact. An electro-magnet in series with the
arc was so located that, when energized, it pulled up the iron tube.
This magnet also held the brass covered iron rod from pushing the
upper carbon down the tube so that the two carbons were pulled apart,
striking the arc. When the arc went out, the iron tube dropped back
into its original position, the brass covered iron rod was released,
pushing the upper carbon down the tube until the two carbons again
touched. This closed the circuit again, striking the arc as before.

[Illustration: ROBERTS’ ARC LAMP, 1852.

The arc was controlled by an electro-magnet which held an iron tube to
which the upper carbon was fastened.]

[Illustration: SLATER AND WATSON’S ARC LAMP, 1852.

Clutches were used for the first time in this arc lamp to feed the
carbons.]

In the same year (1852) Slater and Watson obtained an English patent
on an arc lamp in which the upper carbon was movable and held in place
by two clutches actuated by electro-magnets. The lower carbon was
fixed, and normally the two carbons touched each other. When current
was turned on, the electro-magnet lifted the clutches which gripped the
upper carbon, pulling it up and striking the arc. This was the first
time that a clutch was used to allow the carbon to feed as it became
consumed.

Henry Chapman, in 1855, made an arc in which the upper carbon was
allowed to feed by gravity, but held in place by a chain wound around
a wheel. On this wheel was a brake actuated by an electro-magnet. The
lower carbon was pulled down by an electro-magnet working against a
spring. When no current was flowing or when the arc went out, the two
carbons touched. With current on, one electro-magnet set the brake and
held the upper carbon stationary. The other electro-magnet pulled the
lower carbon down, thus striking the arc.

None of these mechanisms regulated the length of the arc. It was not
until 1856 that Joseph Lacassagne and Henry Thiers, Frenchmen, invented
the so-called “differential” method of control, which made the carbons
feed when the arc voltage, and hence length, became too great. This
principle was used in commercial arc lamps several years afterward when
they were operated on series circuits, as it had the added advantage
of preventing the feeding of one arc lamp affecting another on the
same circuit. This differential control consists in principle of two
electro-magnets, one in series with, and opposing the pull of the other
which is in shunt with the arc. The series magnet pulls the carbons
apart and strikes the arc. As the arc increases in length, its voltage
rises, thereby increasing the current flowing through the shunt magnet.
This increases the strength of the shunt magnet and, when the arc
becomes too long, the strength of the shunt becomes greater than that
of the series magnet, thus making the carbons feed.

[Illustration: DIAGRAM OF “DIFFERENTIAL” METHOD OF CONTROL OF AN ARC
LAMP.

This principle, invented by Lacassagne and Thiers, was used in all arc
lamps when they were commercially introduced on a large scale more than
twenty years later.]

The actual method adopted by Lacassagne and Thiers was different from
this, but it had this principle. They used a column of mercury on
which the lower carbon floated. The upper carbon was stationary. The
height of the mercury column was regulated by a valve connected with
a reservoir of mercury. The pull of the series magnet closed the valve
fixing the height of the column. The pull of the shunt magnet tended
to open the valve, and when it overcame the pull of the series magnet
it allowed mercury to flow from the reservoir, raising the height of
the column bringing the carbons nearer together. This reduced the
arc voltage and shunt magnet strength until the valve closed again.
Thus the carbons were always kept the proper distance apart. In first
starting the arc, or if the arc should go out, current would only flow
through the shunt magnet, bringing the two carbons together until they
touched. Current would then flow through the contact of the two carbons
and through the series magnet, shutting the valve. There were no means
of pulling the carbons apart to strike the arc. Current flowing through
the high resistance of the poor contact of the two carbons, heated
their tips to incandescence. The incandescent tips would begin to burn
away, thus after a time starting an arc. The arc, however, once started
was maintained the proper length.

[Illustration: LACASSAGNE AND THIERS’ DIFFERENTIALLY CONTROLLED ARC
LAMP, 1856.

The lower carbon floated on a column of mercury whose height was
“differentially” controlled by series and shunt magnets.]

In 1857, Serrin took out his first patent on an arc lamp, the general
principles of which were the same as in others he made. The mechanism
consisted of two drums, one double the diameter of the other. Both
carbons were movable, the upper one feeding down, and the lower one
feeding up, being connected with chains wound around the drums. The
difference in consumption of the two carbons was therefore compensated
for by the difference in size of the drums, thus maintaining the
location of the arc in a fixed position. A train of wheels controlled
by a pawl and regulated by an electro-magnet, controlled the movement
of the carbons. The weight of the upper carbon and its holder actuates
the train of wheels.

[Illustration: SERRIN’S ARC LAMP, 1857.

This type of arc was not differentially controlled but was the first
commercial lamp later used. Both carbons were movable, held by chains
wound around drums which were controlled by ratchets actuated by an
electro-magnet.]




DEVELOPMENT OF THE DYNAMO, 1840–1860


During the first few years after 1840 the dynamo was only a laboratory
experiment. Woolrich devised a machine which had several pairs of
magnets and double the number of coils in order to make the current
obtained less pulsating. Wheatstone in 1845 patented the use of
electro-magnets in place of permanent magnets. Brett in 1848 suggested
that the current, generated in the coils, be allowed to flow through
a coil surrounding each permanent magnet to further strengthen the
magnets. Pulvermacher in 1849 proposed the use of thin plates of iron
for the bobbins, to reduce the eddy currents generated in the iron.
Sinsteden in 1851 suggested that the current from a permanent magnet
machine be used to excite the field coils of an electro-magnet machine.

In 1855 Soren Hjorth, of Copenhagen, Denmark, patented a dynamo having
both permanent and electro-magnets, the latter being excited by
currents first induced in the bobbins by the permanent magnets. In 1856
Dr. Werner Siemens invented the shuttle wound armature. This consisted
of a single coil of wire wound lengthwise and counter sunk in a long
cylindrical piece of iron. This revolved between the magnet poles which
were shaped to fit the cylindrical armature.

[Illustration: SIEMENS’ DYNAMO, 1856.

This dynamo was an improvement over others on account of the
construction of its “shuttle” armature.]




THE FIRST COMMERCIAL INSTALLATION OF AN ELECTRIC LIGHT


In 1862 a Serrin type of arc lamp was installed in the Dungeness
lighthouse in England. Current was supplied by a dynamo made by the
Alliance Company, which had been originally designed in 1850 by Nollet,
a professor of Physics in the Military School in Brussels. Nollet’s
original design was of a dynamo having several rows of permanent
magnets mounted radially on a stationary frame, with an equal number
of bobbins mounted on a shaft which rotated and had a commutator so
direct current could be obtained. A company was formed to sell hydrogen
gas for illuminating purposes, the gas to be made by the decomposition
of water with current from this machine. Nollet died and the company
failed, but it was reorganized as the Alliance Company a few years
later to exploit the arc lamp.

[Illustration: ALLIANCE DYNAMO, 1862.

This was the dynamo used in the first commercial installation of an arc
light in the Dungeness Lighthouse, England, 1862.]

About the only change made in the dynamo was to substitute collector
rings for the commutator to overcome the difficulties of commutation.
Alternating current was therefore generated in this first commercial
machine. It had a capacity for but one arc light, which probably
consumed less than ten amperes at about 45 volts, hence delivered
in the present terminology not over 450 watts or about two-thirds
of a horsepower. As the bobbins of the armature undoubtedly had a
considerable resistance, the machine had an efficiency of not over 50
per cent and therefore required at least one and a quarter horsepower
to drive it.




FURTHER DYNAMO DEVELOPMENTS


In the summer of 1886 Sir Charles Wheatstone constructed a self-excited
machine on the principle of using the residual magnetism in the field
poles to set up a feeble current in the armature which, passing through
the field coils, gradually strengthened the fields until they built up
to normal strength. It was later found that this idea had been thought
of by an unknown man, being disclosed by a clause in a provisional
1858 English patent taken out by his agent. Wheatstone’s machine was
shown to the Royal Society in London and a paper on it read before the
Society on February 14, 1867. The field coils were shunt wound.

[Illustration: WHEATSTONE’S SELF-EXCITED DYNAMO, 1866.

This machine was the first self-excited dynamo by use of the residual
magnetism in the field poles.]

Dr. Werner Siemens also made a self-excited machine, having series
fields, a paper on which was read before the Academy of Sciences
in Berlin on January 17, 1867. This paper was forwarded to the
Royal Society in London and presented at the same meeting at which
Wheatstone’s dynamo was described. Wheatstone probably preceded Siemens
in this re-discovery of the principle of self-excitation, but both are
given the merit of it. However, S. A. Varley on December 24, 1866,
obtained a provisional English patent on this, which was not published
until July, 1867.

[Illustration: GRAMME’S DYNAMO, 1871.

These were commercially used, their main feature being the “ring” wound
armature.]

[Illustration: GRAMME’S “RING” ARMATURE.

Wire coils, surrounding an iron wire core, were all connected together
in an endless ring, each coil being tapped with a wire connected to a
commutator bar.]

In 1870 Gramme, a Frenchman, patented his well-known ring armature. The
idea had been previously thought of by Elias, a Hollander, in 1842, and
by Pacinnotti, an Italian, as shown by the crude motors (not dynamos)
they had made. Gramme’s armature consisted of an iron wire core coated
with a bituminous compound in order to reduce the eddy currents. This
core was wound with insulated wire coils, all connected together in
series as one single endless coil. Each coil was tapped with a wire
connected to a commutator bar. His first machine, having permanent
magnets for fields, was submitted to the French Academy of Sciences in
1871. Later machines were made with self-excited field coils, which
were used in commercial service. They had, however a high resistance
armature, so that their efficiency did not exceed 50 per cent.

[Illustration: ALTENECK’S DYNAMO WITH “DRUM” WOUND ARMATURE, 1872.

The armature winding was entirely on the surface of the armature core,
a principle now used in all dynamos.]

Von Hefner Alteneck, an engineer with Siemens, invented the drum wound
armature in 1872. The wires of the armature were all on the surface
of the armature core, the wires being tapped at frequent points for
connection with the commutator bars. Thus in the early seventies,
commercial dynamos were available for use in arc lighting, and a few
installations were made in Europe.




RUSSIAN INCANDESCENT LAMP INVENTORS


In 1872 Lodyguine, a Russian scientist, made an incandescent lamp
consisting of a “V” shaped piece of graphite for a burner, which
operated in nitrogen gas. He lighted the Admiralty Dockyard at St.
Petersburg with about two hundred of these lamps. In 1872 the Russian
Academy of Sciences awarded him a prize of 50,000 rubles (a lot of
real money at that time) for his invention. A company with a capital
of 200,000 rubles (then equal to about $100,000) was formed but as
the lamp was so expensive to operate and had such a short life, about
twelve hours, the project failed.

[Illustration: LODYGUINE’S INCANDESCENT LAMP, 1872.

The burner was made of graphite and operated in nitrogen gas.]

[Illustration: KONN’S INCANDESCENT LAMP, 1875.

In this lamp the graphite rods operated in a vacuum.]

Kosloff, another Russian, in 1875 patented a graphite in nitrogen
incandescent lamp, which had several graphite rods for burners, so
arranged that when one failed another was automatically connected.
Konn, also a Russian, made a lamp similar to Kosloff’s except that
the graphite rods operated in a vacuum. Bouliguine, another Russian,
in 1876 made an incandescent lamp having a long graphite rod, only
the upper part of which was in circuit. As this part burned out, the
rod was automatically pushed up so that a fresh portion then was in
circuit. It operated in a vacuum. None of these lamps was commercial as
they blackened rapidly and were too expensive to maintain.

[Illustration: BOULIGUINE’S INCANDESCENT LAMP, 1876.

A long graphite rod, the upper part of which only was in circuit,
operated in vacuum. As this part burned out, the rod was automatically
shoved up, a fresh portion then being in the circuit.]




THE JABLOCHKOFF “CANDLE”


Paul Jablochkoff was a Russian army officer and an engineer. In the
early seventies he came to Paris and developed a novel arc light. This
consisted of a pair of carbons held together side by side and insulated
from each other by a mineral known as kaolin which vaporized as the
carbons were consumed. There was no mechanism, the arc being started
by a thin piece of carbon across the tips of the carbons. Current
burned this bridge, starting the arc. The early carbons were about
five inches long, and the positive carbon was twice as thick as the
negative to compensate for the unequal consumption on direct current.
This, however, did not work satisfactorily. Later the length of the
carbons was increased, the carbon made of equal thickness and burned
on alternating current of about eight or nine amperes at about 45
volts. He made an alternating current generator which had a stationary
exterior armature with interior revolving field poles. Several
“candles,” as they were called, were put in one fixture to permit all
night service and an automatic device was developed, located in each
fixture, so that should one “candle” go out for any reason, another was
switched into service.

[Illustration: JABLOCHKOFF “CANDLE,” 1876.

This simple arc consisted of a pair of carbons held together side by
side and insulated from each other by kaolin. Several boulevards in
Paris were lighted with these arc lights. This arc lamp is in the
collection of the Smithsonian Institution.]

In 1876 many of these “candles” were installed and later several of the
boulevards in Paris were lighted with them. This was the first large
installation of the arc light, and was the beginning of its commercial
introduction. Henry Wilde made some improvements in the candle by
eliminating the kaolin between the carbons which gave Jablochkoff’s arc
its peculiar color. Wilde’s arc was started by allowing the ends of the
carbons to touch each other, a magnet swinging them apart thus striking
the arc.

[Illustration: JABLOCHKOFF’S ALTERNATING CURRENT DYNAMO, 1876.

This dynamo had a stationary exterior armature and internal revolving
field poles. Alternating current was used for the Jablochkoff “candle”
to overcome the difficulties of unequal consumption of the carbons on
direct current.]


COMMERCIAL INTRODUCTION OF THE DIFFERENTIALLY CONTROLLED ARC LAMP

About the same time Lontin, a Frenchman, improved Serrin’s arc lamp
mechanism by the application of series and shunt magnets. This is the
differential principle which was invented by Lacassagne and Thiers in
1855 but which apparently had been forgotten. Several of these lamps
were commercially installed in France beginning with 1876.




ARC LIGHTING IN THE UNITED STATES


[Illustration: WALLACE-FARMER ARC LAMP, 1875.

This “differentially controlled” arc lamp consisted of two slabs of
carbon between which the arc played. In the original lamp the carbon
slabs were mounted on pieces of wood held in place by bolts, adjustment
being made by hitting the upper carbon slab with a hammer. This lamp is
in the collection of the Smithsonian Institution.]

[Illustration: WALLACE-FARMER DYNAMO, 1875.

This was the first commercial dynamo used in the United States for
arc lighting. This dynamo is in the collection of the Smithsonian
Institution.]

About 1875 William Wallace of Ansonia, Connecticut, made an arc light
consisting of two rectangular carbon plates mounted on a wooden frame.
The arc played between the two edges of the plates, which lasted much
longer than rods. When the edges had burned away so that the arc then
became unduly long, the carbon plates were brought closer together by
hitting them with a hammer. Wallace became associated with Moses G.
Farmer, and they improved this crude arc by fastening the upper carbon
plate to a rod which was held by a clutch controlled by a magnet. This
magnet had two coils in one, the inner winding in series with the arc,
and outer one in shunt and opposing the series winding. The arc was
therefore differentially controlled.

[Illustration: WESTON’S ARC LAMP, 1876.

This lamp is in the collection of the Smithsonian Institution.]

They also developed a series wound direct current dynamo. The armature
consisted of a number of bobbins, all connected together in an endless
ring. Each bobbin was also connected to a commutator bar. There were
two sets of bobbins, commutators and field poles, the equivalent of two
machines in one, which could be connected either to separate circuits,
or together in series on one circuit. The Wallace-Farmer system was
commercially used. The arc consumed about 20 amperes at about 35 volts,
but as the carbon plates cooled the arc, the efficiency was poor.
The arc flickered back and forth on the edges of the carbons casting
dancing shadows. The carbons, while lasting about 50 hours, were not
uniform in density, so the arc would flare up and cast off soot and
sparks.

Edward Weston of Newark, New Jersey, also developed an arc lighting
system. His commercial lamp had carbon rods, one above the other, and
the arc was also differentially controlled. An oil dash pot prevented
undue pumping of the carbons. His dynamo had a drum-wound armature, and
had several horizontal field coils on each side of one pair of poles
between which the armature revolved. The system was designed for about
20 amperes, each are taking about 35 volts.

[Illustration: BRUSH’S DYNAMO, 1877.

This dynamo was used for many years for commercial arc lighting.]

[Illustration: DIAGRAM OF BRUSH ARMATURE.

The armature was not a closed circuit. For description of its
operation, see text.]

Charles F. Brush made a very successful arc lighting system in 1878.
His dynamo was unique in that the armature had eight coils, one end of
each pair of opposite coils being connected together and the other ends
connected to a commutator segment. Thus the armature itself was not a
closed circuit. The machine had two pairs of horizontal poles between
which the coils revolved. One end of the one pair of coils in the most
active position was connected, by means of two of the four brushes,
in series with one end of the two pairs of coils in the lesser active
position. The latter two pairs of coils were connected in multiple
with each other by means of the brushes touching adjacent commutator
segments. The outside circuit was connected to the other two brushes,
one of which was connected to the other end of the most active pair
of coils. The other brush was connected to the other end of the two
lesser active pairs of coils. The one pair of coils in the least active
position was out of circuit. The field coils were connected in series
with the outside circuit.

[Illustration: BRUSH’S ARC LAMP, 1877.

The carbons were differentially controlled. This lamp was used for many
years. This lamp is in the collection of the Smithsonian Institution.]

Brush’s arc lamp was also differentially controlled. It was designed
for about 10 amperes at about 45 volts. The carbons were copper
plated to increase their conductivity. Two pairs of carbons were used
for all-night service, each pair lasting about eight hours. A very
simple device was used to automatically switch the arc from one to
the other pair of carbons, when the first pair was consumed. This
device consisted of a triangular-shaped piece of iron connected to the
solenoid controlling the arc. There was a groove on each of the outer
two corners of this triangle, one groove wider than the other. An iron
washer surrounded each upper carbon. The edge of each washer rested
in a groove. The washer in the narrow groove made a comparatively
tight fit about its carbon. The other washer in the wider groove had
a loose fit about its carbon. Pins prevented the washer from falling
below given points. Both pairs of carbons touched each other at the
start. When current was turned on, the solenoid lifted the triangle,
the loose-fitting washer gripped its carbon first, so that current then
only passed through the other pair of carbons which were still touching
each other. The further movement of the solenoid then separated these
carbons, the arc starting between them. When this pair of carbons
became consumed, they could not feed any more so that the solenoid
would then allow the other pair of carbons to touch, transferring the
arc to that pair.

[Illustration: THOMSON-HOUSTON ARC DYNAMO, 1878.

This dynamo was standard for many years. This machine is in the
collection of the Smithsonian Institution.]

Elihu Thomson and Edwin J. Houston in 1878 made a very successful and
complete arc light system. Their dynamo was specially designed to fit
the requirements of the series arc lamp. The Thomson-Houston machine
was a bipolar, having an armature consisting of three coils, one end of
each of the three coils having a common terminal, or “Y” connected, as
it is called. The other end of each coil was connected to a commutator
segment. The machine was to a great extent self-regulating, that is the
current was inherently constant with fluctuating load, as occurs when
the lamps feed or when the number of lamps burning at one time should
change for any reason. This regulation was accomplished by what is
called “armature reaction,” which is the effect the magnetization of
the armature has on the field strength. Close regulation was obtained
by a separate electro-magnet, in series with the circuit, which shifted
the brushes as the load changed. As there were but three commutator
segments, one for each coil, excessive sparking was prevented by an air
blast.

[Illustration: DIAGRAM OF T-H ARC LIGHTING SYSTEM.]

The “T-H” (Thompson-Houston) lamp employed the shunt feed principle.
The carbons were normally separated, being in most types drawn apart
by a spring. A high resistance magnet, shunted around the arc, served
to draw the carbons together. This occurred on starting the lamp and
thereafter the voltage of the arc was held constant by the balance
between the spring and the shunt magnet. As the carbon burned away the
mechanism advanced to a point where a clutch was tripped, the carbons
brought together, and the cycle repeated. Both the T-H and Brush
systems were extensively used in street lighting, for which they were
the standard when the open arc was superseded by the enclosed.




OTHER AMERICAN ARC LIGHT SYSTEMS


[Illustration: THOMSON-HOUSTON ARC LAMP, 1878.

This is an early model with a single pair of carbons.]

[Illustration: THOMSON DOUBLE CARBON ARC LAMP.

This later model, having two pairs of carbons, was commercially used
for many years. This lamp is in the collection of the Smithsonian
Institution.]

Beginning with about 1880, several arc light systems were developed.
Among these were the Vanderpoele, Hochausen, Waterhouse, Maxim,
Schuyler and Wood. The direct current carbon arc is inherently more
efficient than the alternating current lamp, owing to the fact that the
continuous flow of current in one direction maintains on the positive
carbon a larger crater at the vaporizing point of carbon. This source
furnishes the largest proportion of light, the smaller crater in the
negative carbon much less. With the alternating current arc, the large
crater is formed first on the upper and then on the lower carbon. On
account of the cooling between alternations, the mean temperature falls
below the vaporizing point of carbon, thus accounting for the lower
efficiency of the alternating current arc.

[Illustration: MAXIM DYNAMO.

This dynamo is in the collection of the Smithsonian Institution.]

For this reason all these systems used direct current and the 10 ampere
ultimately displaced the 20 ampere system. The 10 ampere circuit
was later standardized at 9.6 amperes, 50 volts per lamp. The lamp
therefore consumed 480 watts giving an efficiency of about 15 lumens
per watt. This lamp gave an average of 575 candlepower (spherical) in
all directions, though it was called the 2000 cp (candlepower) arc as
under the best possible conditions it could give this candlepower in
one direction. Later a 6.6 ampere arc was developed. This was called
the “1200 cp” lamp and was not quite as efficient as the 9.6 ampere
lamp.




“SUB-DIVIDING THE ELECTRIC LIGHT”


While the arc lamp was being commercially established, it was at once
seen that it was too large a unit for household use. Many inventors
attacked the problem of making a smaller unit, or, as it was called,
“sub-dividing the electric light.” In the United States there were four
men prominent in this work: William E. Sawyer, Moses G. Farmer, Hiram
S. Maxim and Thomas A. Edison. These men did not make smaller arc lamps
but all attempted to make an incandescent lamp that would operate on
the arc circuits.

[Illustration: SAWYER’S INCANDESCENT LAMP, 1878.

This had a graphite burner operating in nitrogen gas.]

[Illustration: FARMER’S INCANDESCENT LAMP, 1878.

The graphite burner operated in nitrogen gas. This lamp is in the
collection of the Smithsonian Institution.]

Sawyer made several lamps in the years 1878–79 along the lines of the
Russian scientists. All his lamps had a thick carbon burner operating
in nitrogen gas. They had a long glass tube closed at one end and the
other cemented to a brass base through which the gas was put in. Heavy
fluted wires connected the burner with the base to radiate the heat,
in order to keep the joint in the base cool. The burner was renewable
by opening the cemented joint. Farmer’s lamp consisted of a pair of
heavy copper rods mounted on a rubber cork, between which a graphite
rod was mounted. This was inserted in a glass bulb and operated in
nitrogen gas. Maxim made a lamp having a carbon burner operating in a
rarefied hydrocarbon vapor. He also made a lamp consisting of a sheet
of platinum operating in air.




EDISON’S INVENTION OF A PRACTICAL INCANDESCENT LAMP


Edison began the study of the problem in the spring of 1878. He had a
well-equipped laboratory at Menlo Park, New Jersey, with several able
assistants and a number of workmen, about a hundred people all told.
He had made a number of well-known inventions, among which were the
quadruplex telegraph whereby four messages could be sent simultaneously
over one wire, the carbon telephone transmitter without which Bell’s
telephone receiver would have been impracticable, and the phonograph.
All of these are in use today, so Edison was eminently fitted to attack
the problem.

[Illustration: MAXIM’S INCANDESCENT LAMP, 1878.

The carbon burner operated in a rarefied hydrocarbon vapor. This lamp
is in the collection of the Smithsonian Institution.]

Edison’s first experiments were to confirm the failures of other
experimenters. Convinced of the seeming impossibility of carbon, he
turned his attention to platinum as a light giving element. Realizing
the importance of operating platinum close to its melting temperature,
he designed a lamp which had a thermostatic arrangement so that
the burner would be automatically short circuited the moment its
temperature became dangerously close to melting. The burner consisted
of a double helix of platinum wire within which was a rod. When the
temperature of the platinum became too high, the rod in expanding
would short circuit the platinum. The platinum cooled at once, the
rod contracted opening the short circuit and allowing current to flow
through the burner again. His first incandescent lamp patent covered
this lamp. His next patent covered a similar lamp with an improved
thermostat consisting of an expanding diaphragm. Both of these lamps
were designed for use on series circuits.

[Illustration: EDISON’S FIRST EXPERIMENTAL LAMP, 1878.

The burner was a coil of platinum wire which was protected from
operating at too high a temperature by a thermostat.]

The only system of distributing electricity, known at that time, was
the series system. In this system current generated in the dynamo
armature flowed through the field coils, out to one lamp after another
over a wire, and then back to the dynamo. There were no means by which
one lamp could be turned on and off without doing the same with all the
others on the circuit. Edison realized that while this was satisfactory
for street lighting where arcs were generally used, it never would
be commercial for household lighting. He therefore decided that a
practical incandescent electric lighting system must be patterned
after gas lighting with which it would compete. He therefore made
an intensive study of gas distribution and reasoned that a constant
pressure electrical system could be made similar to that of gas.

The first problem was therefore to design a dynamo that would give a
constant pressure instead of constant current. He therefore reasoned
that the internal resistance of the armature must be very low or the
voltage would fall as current was taken from the dynamo. Scientists
had shown that the most economical use of electricity from a primary
battery was where the external resistance of the load was the same as
the internal resistance of the battery, or in other words, 50 per cent
was the maximum possible efficiency.

[Illustration: DIAGRAM OF CONSTANT CURRENT SERIES SYSTEM.

This, in 1878, was the only method of distributing electric current.]

[Illustration: DIAGRAM OF EDISON’S MULTIPLE SYSTEM, 1879.

Edison invented the multiple system of distributing electric current,
now universally used.]

When Edison proposed a very low resistance armature so that the dynamo
would have an efficiency of 90 per cent at full load, he was ridiculed.
Nevertheless he went ahead and made one which attained this. The
armature consisted of drum-wound insulated copper rods, the armature
core having circular sheets of iron with paper between to reduce the
eddy currents. There were two vertical fields above and connected in
shunt with the armature. It generated electricity at about a hundred
volts constant pressure and could supply current up to about 60
amperes at this pressure. It therefore had a capacity, in the present
terminology, of about 6 kilowatts (or 8 horsepower).

[Illustration: EDISON DYNAMO, 1879.

Edison made a dynamo that was 90 per cent efficient which scientists
said was impossible. This dynamo is in the collection of the
Smithsonian Institution and was one of the machines on the steamship
Columbia, the first commercial installation of the Edison lamp.]

A multiple system of distribution would make each lamp independent of
every other and with a dynamo made for such a system, the next thing
was to design a lamp for it. Having a pressure of about a hundred volts
to contend with, the lamp, in order to take a small amount of current,
must, to comply with Ohm’s law, have a high resistance. He therefore
wound many feet of fine platinum wire on a spool of pipe clay and
made his first high resistance lamp. He used his diaphragm thermostat
to protect the platinum from melting, and, as now seems obvious but
was not to all so-called electricians at that time, the thermostat
was arranged to open circuit instead of short circuit the burner when
it became too hot. This lamp apparently solved the problem, and, in
order to protect the platinum from the oxygen of the air, he coated
it with oxide of zirconium. Unfortunately zirconia, while an insulator
at ordinary temperatures, becomes, as is now known, a conductor of
electricity when heated, so that the lamp short circuited itself when
it was lighted.

[Illustration: EDISON’S HIGH RESISTANCE PLATINUM LAMP, 1879.

This lamp had a high resistance burner, necessary for the multiple
system.]

[Illustration: EDISON’S HIGH RESISTANCE PLATINUM IN VACUUM LAMP, 1879.

This experimental lamp led to the invention of the successful carbon
filament lamp.]

During his experiments he had found that platinum became exceedingly
hard after it had been heated several times to incandescence by current
flowing through it. This apparently raised its melting temperature so
he was able to increase the operating temperature and therefore greatly
increase the candlepower of his lamps after they had been heated a few
times. Examination of the platinum under a microscope showed it to be
much less porous after heating, so he reasoned that gases were occluded
throughout the platinum and were driven out by the heat. This led him
to make a lamp with a platinum wire to operate in vacuum, as he thought
that more of the occluded gases would come out under such circumstances.

[Illustration: EDISON’S CARBON LAMP OF OCTOBER 21, 1879.

This experimental lamp, having a high resistance carbon filament
operating in a high vacuum maintained by an all-glass globe, was the
keystone of Edison’s successful incandescent lighting system. All
incandescent lamps made today embody the basic features of this lamp.
This replica is in the Smithsonian Institution exhibit of Edison lamps.
The original was destroyed.]

These lamps were expensive to make, and, knowing that he could get the
requisite high resistance at much less cost from a long and slender
piece of carbon, he thought he might be able to make the carbon last
in the high vacuum he had been able to obtain from the newly invented
Geissler and Sprengel mercury air pumps. After several trials he
finally was able to carbonize a piece of ordinary sewing thread. This
he mounted in a one-piece all glass globe, all joints fused by melting
the glass together, which he considered was essential in order to
maintain the high vacuum. Platinum wires were fused in the glass to
connect the carbonized thread inside the bulb with the circuit outside
as platinum has the same coefficient of expansion as glass and hence
maintains an airtight joint. He reasoned that there would be occluded
gases in the carbonized thread which would immediately burn up if the
slightest trace of oxygen were present, so he heated the lamp while it
was still on the exhaust pump after a high degree of vacuum had been
obtained. This was accomplished by passing a small amount of current
through the “filament,” as he called it, gently heating it. Immediately
the gases started coming out, and it took eight hours more on the pump
before they stopped. The lamp was then sealed and ready for trial.

[Illustration: DEMONSTRATION OF EDISON’S INCANDESCENT LIGHTING SYSTEM.

Showing view of Menlo Park Laboratory Buildings, 1880.]

On October 21, 1879, current was turned into the lamp and it lasted
forty-five hours before it failed. A patent was applied for on November
4th of that year and granted January 27, 1880. All incandescent lamps
made today embody the basic features of this lamp. Edison immediately
began a searching investigation of the best material for a filament and
soon found that carbonized paper gave several hundred hours life. This
made it commercially possible, so in December, 1879, it was decided
that a public demonstration of his incandescent lighting system should
be made. Wires were run to several houses in Menlo Park, N. J., and
lamps were also mounted on poles, lighting the country roads in the
neighborhood. An article appeared in the New York Herald on Sunday,
December 21, 1879, describing Edison’s invention and telling of the
public demonstration to be given during the Christmas holidays. This
occupied the entire first page of the paper, and created such a furor
that the Pennsylvania Railroad had to run special trains to Menlo
Park to accommodate the crowds. The first commercially successful
installation of the Edison incandescent lamps and lighting system was
made on the steamship Columbia, which started May 2, 1880, on a voyage
around Cape Horn to San Francisco, Calif.

The carbonized paper filament of the first commercial incandescent lamp
was quite fragile. Early in 1880 carbonized bamboo was found to be not
only sturdy but made an even better filament than paper. The shape of
the bulb was also changed from round to pear shape, being blown from
one inch tubing. Later the bulbs were blown directly from molten glass.

[Illustration: DYNAMO ROOM, S. S. COLUMBIA.

The first commercial installation of the Edison Lamp, started May 2,
1880. One of these original dynamos is on exhibit at the Smithsonian
Institution.]

As it was inconvenient to connect the wires to the binding posts of
a new lamp every time a burned out lamp had to be replaced, a base
and socket for it were developed. The earliest form of base consisted
simply of bending the two wires of the lamp back on the neck of the
bulb and holding them in place by wrapping string around the neck. The
socket consisted of two pieces of sheet copper in a hollow piece of
wood. The lamp was inserted in this, the two-wire terminals of the lamp
making contact with the two-sheet copper terminals of the socket, the
lamp being rigidly held in the socket by a thumb screw which forced
the socket terminals tight against the neck of the bulb.

[Illustration: ORIGINAL SOCKET FOR INCANDESCENT LAMPS, 1880.]

[Illustration: WIRE TERMINAL BASE LAMP, 1880.

This crude form of lamp base fitted the original form of lamp socket
pictured above. This lamp is in the exhibit of Edison lamps in the
Smithsonian Institution.]

This crude arrangement was changed in the latter part of 1880 to a
screw shell and a ring for the base terminals, wood being used for
insulation. The socket was correspondingly changed. This was a very
bulky affair, so the base was changed to a cone-shaped ring and a
screw shell for terminals. Wood was used for insulation, which a short
time after was changed to plaster of Paris as this was also used to
fasten the base to the bulb. It was soon found that the tension created
between the two terminals of the base when the lamp was firmly screwed
in the socket often caused the plaster base to pull apart, so the shape
of the base was again changed early in 1881, to the form in use today.

An improved method of connecting the ends of the filament to the
leading-in wires was adopted early in 1881. Formerly this was
accomplished by a delicate clamp having a bolt and nut. The improvement
consisted of copper plating the filament to the leading-in wire.

[Illustration: ORIGINAL SCREW BASE LAMP, 1880.

This first screw base, consisting of a screw shell and ring for
terminals with wood for insulation, was a very bulky affair. This lamp
is in the exhibit of Edison lamps in the Smithsonian Institution.]

[Illustration: IMPROVED SCREW BASE LAMP, 1881.

The terminals of this base consisted of a cone shaped ring and a screw
shell. At first wood was used for insulation, later plaster of paris
which was also used to fasten the base to the bulb. This lamp is in the
exhibit of Edison lamps in the Smithsonian Institution.]

In the early part of the year 1881 the lamps were made “eight to
the horsepower.” Each lamp, therefore, consumed a little less than
100 watts, and was designed to give 16 candlepower in a horizontal
direction. The average candlepower (spherical) in all directions was
about 77 per cent of this, hence as the modern term “lumen” is 12.57
spherical candlepower, these lamps had an initial efficiency of about
1.7 lumens per watt. The lamps blackened considerably during their life
so that just before they burned out their candlepower was less than
half that when new. Thus their mean efficiency throughout life was
about 1.1 l-p-w (lumens per watt). These figures are interesting in
comparison with the modern 100-watt gas-filled tungsten-filament lamp
which has an initial efficiency of 12.9, and a mean efficiency of 11.8,
l-p-w. In other words the equivalent (wattage) size of modern lamp
gives over seven times when new, and eleven times on the average, as
much light for the same energy consumption as Edison’s first commercial
lamp. In the latter part of 1881 the efficiency was changed to “ten
lamps per horsepower,” equivalent to 2¼ l-p-w initially. Two sizes of
lamps were made: 16 cp for use on 110-volt circuits and 8 cp for use
either direct on 55 volts or two in series on 110-volt circuits.

[Illustration: FINAL FORM OF SCREW BASE, 1881.

With plaster of paris, the previous form of base was apt to pull apart
when the lamp was firmly screwed into the socket. The form of the base
was therefore changed to that shown, which overcame these difficulties,
and which has been used ever since. The lamp shown was standard for
three years and is in the exhibit of Edison lamps in the Smithsonian
Institution.]




EDISON’S THREE-WIRE SYSTEM


The distance at which current can be economically delivered at 110
volts pressure is limited, as will be seen from a study of Ohm’s law.
The loss of power in the distributing wires is proportional to the
square of the current flowing. If the voltage be doubled, the amount
of current is halved, for a given amount of electric power delivered,
so that the size of the distributing wires can then be reduced to
one-quarter for a given loss in them. At that time (1881) it was
impossible to make 220-volt lamps, and though they are now available,
their use is uneconomical, as their efficiency is much poorer than that
of 110-volt incandescent lamps.

Edison invented a distributing system that had two 110-volt circuits,
with one wire called the neutral, common to both circuits so that the
pressure on the two outside wires was 220 volts. The neutral wire had
only to be large enough to carry the difference between the currents
flowing in the two circuits. As the load could be so arranged that it
would be approximately equal at all times on both circuits, the neutral
wire could be relatively small in size. Thus the three-wire system
resulted in a saving of 60 per cent in copper over the two-wire system
or, for the same amount of copper, the distance that current could be
delivered was more than doubled.

[Illustration: DIAGRAM OF EDISON’S THREE-WIRE SYSTEM, 1881.

This system reduced the cost of copper in the multiple distributing
system 60 per cent.]


DEVELOPMENT OF THE ALTERNATING CURRENT CONSTANT POTENTIAL SYSTEM

The distance that current can be economically distributed, as has
been shown, depends upon the voltage used. If, therefore, current
could be sent out at a high voltage and the pressure brought down to
that desired at the various points to which it is distributed, such
distribution could cover a much greater area. Lucien Gaulard was a
French inventor and was backed by an Englishman named John D. Gibbs.
About 1882 they patented a series alternating-current system of
distribution. They had invented what is now called a transformer which
consisted of two separate coils of wire mounted on an iron core. All
the primary coils were connected in series, which, when current went
through them, induced a current in the secondary coils. Lamps were
connected in multiple on each of the secondary coils. An American
patent was applied for on the transformer, but was refused on the basis
that “more current cannot be taken from it than is put in.” While
this is true if the word energy were used, the transformer can supply
a greater current at a lower voltage (or vice versa) than is put in,
the ratio being in proportion to the relative number of turns in the
primary and secondary coils. The transformer was treated with ridicule
and Gaulard died under distressing circumstances.

[Illustration: DIAGRAM OF STANLEY’S ALTERNATING CURRENT MULTIPLE
SYSTEM, 1885.

This system is now universally used for distributing electric current
long distances.]

Information regarding the transformer came to the attention of
William Stanley, an American, in the latter part of 1885. He made an
intensive study of the scheme, and developed a transformer in which
the primary coil was connected in multiple on a constant potential
alternating-current high-voltage system. From the secondary coil a
lower constant voltage was obtained. An experimental installation
was made at Great Barrington, Mass., in the early part of 1886, the
first commercial installation being made in Buffalo, New York, in the
latter part of the year. This scheme enabled current to be economically
distributed to much greater distances. The voltage of the high-tension
circuit has been gradually increased as the art has progressed from
about a thousand volts to over two hundred thousand volts pressure in a
recent installation in California, where electric power is transmitted
over two hundred miles.




INCANDESCENT LAMP DEVELOPMENTS, 1884–1894


In 1884 the ring of plaster around the top of the base was omitted; in
1886 an improvement was made by pasting the filament to the leading-in
wires with a carbon paste instead of the electro-plating method; and
in 1888 the length of the base was increased so that it had more
threads. Several concerns started making incandescent lamps, the
filaments being made by carbonizing various substances. “Parchmentized”
thread consisted of ordinary thread passed through sulphuric acid.
“Tamadine” was cellulose in the sheet form, punched out in the shape
of the filament. Squirted cellulose in the form of a thread was also
used. This was made by dissolving absorbent cotton in zinc chloride,
the resulting syrup being squirted through a die into alcohol which
hardened the thread thus formed. This thread was washed in water, dried
in the air and then cut to proper length and carbonized.

[Illustration: STANDARD EDISON LAMP, 1884.

The ring of plaster around the neck of previous lamps was omitted. This
lamp is in the exhibit of Edison lamps in the Smithsonian Institution.]

[Illustration: STANDARD EDISON LAMP, 1888.

The length of the base was increased so it had more threads. This lamp
is in the exhibit of Edison lamps in the Smithsonian Institution.]

The filament was improved by coating it with graphite. One method,
adopted about 1888, was to dip it in a hydrocarbon liquid before
carbonizing. Another, more generally adopted in 1893 was a process
originally invented by Sawyer, one of the Americans who had attempted
to “sub-divide the electric light” in 1878–79. This process consisted
of passing current through a carbonized filament in an atmosphere of
hydrocarbon vapor. The hot filament decomposed the vapor, depositing
graphite on the filament. The graphite coated filament improved it so
it could operate at 3½ lumens per watt (initial efficiency). Lamps of
20, 24, 32 and 50 candlepower were developed for 110-volt circuits.
Lamps in various sizes from 12 to 36 cp were made for use on storage
batteries having various numbers of cells and giving a voltage of
from 20 to 40 volts. Miniature lamps of from ½ to 2 cp for use on dry
batteries of from 2½ to 5½ volts, and 3 to 6 cp on 5½ to 12 volts, were
also made. These could also be connected in series on 110 volts for
festoons. Very small lamps of ½ cp of 2 to 4 volts for use in dentistry
and surgery were made available. These miniature lamps had no bases,
wires being used to connect them to the circuit.

[Illustration: STANDARD EDISON LAMP, 1894.

This lamp had a “treated” cellulose filament, permitting an efficiency
of 3½ lumens per watt which has never been exceeded in a carbon
lamp. This lamp is in the exhibit of Edison lamps in the Smithsonian
Institution.]

Lamps for 220-volt circuits were developed as this voltage was
desirable for power purposes, electric motors being used, and a few
lamps were needed on such circuits. They are less efficient and more
expensive than 110-volt lamps, their use being justified however
only when it is uneconomical to have a separate 110-volt circuit for
lighting. The lamps were made in sizes from 16 to 50 candlepower.

[Illustration:

  Edison.            Thomson-Houston.   Westinghouse.      Brush-Swan.

  Edi-Swan           Edi-Swan           United States.     Hawkeye.
  (single contact).  (double contact).

  Ft. Wayne Jenny.            Mather or Perkins.       Loomis.

  Schaeffer or National.      Indianapolis Jenny.      Siemens & Halske.

VARIOUS STANDARD BASES IN USE, 1892.]

[Illustration: THOMSON-HOUSTON SOCKET.]

[Illustration: WESTINGHOUSE SOCKET.]

Electric street railway systems used a voltage in the neighborhood of
550, and lamps were designed to burn five in series on this voltage.
These lamps were different from the standard 110-volt lamps although
they were made for about this voltage. As they were burned in series,
the lamps were selected to operate at a definite current instead of
at a definite voltage, so that the lamps when burned in series would
operate at the proper temperature to give proper life results. Such
lamps would therefore vary considerably in individual volts, and
hence would not give good service if burned on 110-volt circuits. The
candelabra screw base and socket and the miniature screw base and
socket were later developed. Ornamental candelabra base lamps were made
for use direct on 110 volts, smaller sizes being operated in series
on this voltage. The former gave about 10 cp, the latter in various
sizes from 4 to 8 cp. The miniature screw base lamps were for low volt
lighting.

[Illustration:

  Thomson-Houston.      Westinghouse.

ADAPTERS FOR EDISON SCREW SOCKETS, 1892.

Next to the Edison base, the Thomson-Houston and Westinghouse bases
were the most popular. By use of these adapters, Edison base lamps
could be used in T-H and Westinghouse sockets.]

The various manufacturers of lamps in nearly every instance made bases
that were very different from one another. No less than fourteen
different standard bases and sockets came into commercial use.
These were known as, Brush-Swan, Edison, Edi-Swan (double contact),
Edi-Swan (single contact), Fort Wayne Jenny, Hawkeye, Indianapolis
Jenny, Loomis, Mather or Perkins, Schaeffer or National, Siemens &
Halske, Thomson-Houston, United States and Westinghouse. In addition
there were later larger sized bases made for use on series circuits.
These were called the Bernstein, Heisler, Large Edison, Municipal
Bernstein, Municipal Edison, Thomson-Houston (alternating circuit) and
Thomson-Houston (arc circuit). Some of these bases disappeared from
use and in 1900 the proportion in the United States was about 70 per
cent Edison, 15 per cent Westinghouse, 10 per cent Thomson-Houston
and 5 per cent for all the others remaining. A campaign was started
to standardize the Edison base, adapters being sold at cost for the
Westinghouse and Thomson-Houston sockets so that Edison base lamps
could be used. In a few years the desired results were obtained so that
now there are no other sockets in the United States but the Edison
screw type for standard lighting service. This applies also to all
other countries in the world except England where the bayonet form of
base and socket is still popular.

[Illustration:

  Bernstein.           Heisler.               Thomson-Houston
                                              (alternating current).

  Thomson-Houston      Municipal Edison.      Municipal Bernstein.
  (arc circuit).

VARIOUS SERIES BASES IN USE, 1892.

The above six bases have been superseded by the “Large Edison,” now
called the Mogul Screw base.]




THE EDISON “MUNICIPAL” STREET LIGHTING SYSTEM




[Illustration: EDISON “MUNICIPAL” SYSTEM, 1885.


High voltage direct current was generated, several circuits operating
in multiple, three ampere lamps burning in series on each circuit.
Photograph courtesy of Association of Edison Illuminating Companies.]

The arc lamp could not practically be made in a unit smaller than
the so-called “1200 candlepower” (6.6 ampere) or “half” size, which
really gave about 350 spherical candlepower. A demand therefore arose
for a small street lighting unit, and Edison designed his “Municipal”
street lighting system to fill this requirement. His experience in the
making of dynamos enabled him to make a direct current bipolar constant
potential machine that would deliver 1000 volts which later was
increased to 1200 volts. They were first made in two sizes having an
output of 12 and 30 amperes respectively. Incandescent lamps were made
for 3 amperes in several sizes from 16 to 50 candlepower. These lamps
were burned in series on the 1200-volt direct current system. Thus the
12-ampere machine had a capacity for four series circuits, each taking
3 amperes, the series circuits being connected in multiple across the
1200 volts. The number of lamps on each series circuit depended upon
their size, as the voltage of each lamp was different for each size,
being about 1½ volts per cp.

A popular size was the 32-candlepower unit, which therefore required
about 45 volts and hence at 3 amperes consumed about 135 watts.
Allowing 5 per cent loss in the wires of each circuit, there was
therefore 1140 of the 1200 volts left for the lamps. Hence about 25
32-candlepower or 50 16-candlepower lamps could be put on each series
circuit. Different sizes of lamps could also be put on the same
circuit, the number depending upon the aggregate voltage of the lamps.

[Illustration: EDISON MUNICIPAL LAMP, 1885.

Inside the base was an arrangement by which the lamp was automatically
short circuited when it burned out.]

A device was put in the base of each lamp to short circuit the lamp
when it burned out so as to prevent all the other lamps on that circuit
from going out. This device consisted of a piece of wire put inside
the lamp bulb between the two ends of the filament. Connected to this
wire was a very thin wire inside the base which held a piece of metal
compressed against a spring. The spring was connected to one terminal
of the base. Should the lamp burn out, current would jump from the
filament to the wire in the bulb, and the current then flowed through
the thin wire to the other terminal of the base. The thin wire was
melted by the current, and the spring pushed the piece of metal up
short circuiting the terminals of the base. This scheme was later
simplified by omitting the wire, spring, etc., and substituting a piece
of metal which was prevented from short circuiting the terminals of
the base by a thin piece of paper. When the lamp burned out the entire
1200 volts was impressed across this piece of paper, puncturing it and
so short circuiting the base terminals. Should one or more lamps go
out on a circuit, the increase in current above the normal 3 amperes
was prevented by an adjustable resistance, or an extra lot of lamps
which could be turned on one at a time, connected to each circuit and
located in the power station under the control of the operator. This
system disappeared from use with the advent of the constant current
transformer.




THE SHUNT BOX SYSTEM FOR SERIES INCANDESCENT LAMPS


[Illustration: SHUNT BOX SYSTEM, 1887.

Lamps were burned in series on a high voltage alternating current, and
when a lamp burned out all the current then went through its “shunt
box,” a reactance coil in multiple with each lamp.]

Soon after the commercial development of the alternating current
constant potential system, a scheme was developed to permit the use
of lamps in series on such circuits without the necessity for short
circuiting a lamp should it burn out. A reactance, called a “shunt box”
and consisting of a coil of wire wound on an iron core, was connected
across each lamp. The shunt box consumed but little current while the
lamp was burning. Should one lamp go out, the entire current would
flow through its shunt box and so maintain the current approximately
constant. It had the difficulty, however, that if several lamps went
out, the current would be materially increased tending to burn out the
remaining lamps on the circuit. This system also disappeared from use
with the development of the constant current transformer.




THE ENCLOSED ARC LAMP


Up to 1893 the carbons of an arc lamp operated in the open air, so
that they were rapidly consumed, lasting from eight to sixteen hours
depending on their length and thickness. Louis B. Marks, an American,
found that by placing a tight fitting globe about the arc, the life
of the carbons was increased ten to twelve times. This was due to the
restricted amount of oxygen of the air in the presence of the hot
carbon tips and thus retarded their consumption. The amount of light
was somewhat decreased, but this was more than offset by the lesser
expense of trimming which also justified the use of more expensive
better quality carbons. Satisfactory operation required that the arc
voltage be increased to about 80 volts.

[Illustration: ENCLOSED ARC LAMP, 1893.

Enclosing the arc lengthened the life of the carbons, thereby greatly
reducing the cost of maintenance.]

This lamp rapidly displaced the series open arc. An enclosed arc lamp
for use on 110-volt constant potential circuits was also developed. A
resistance was put in series with the arc for use on 110-volt direct
current circuits, to act as a ballast in order to prevent the arc from
taking too much current and also to use up the difference between the
arc voltage (80) and the line voltage (110). On alternating current, a
reactance was used in place of the resistance.

The efficiencies in lumens per watt of these arcs (with clear
glassware), all of which have now disappeared from the market, were
about as follows:

  6.6 ampere 510 watt direct current (D.C.) series arc, 8¼ l-p-w.
  5.0 ampere 550 watt direct current multiple (110-volt) arc, 4½ l-p-w.
  7.5 ampere 540 watt alternating current (A.C.) multiple (110-volt)
        arc, 4¼ l-p-w.

[Illustration: OPEN FLAME ARC LAMP, 1898.

Certain salts impregnated in the carbons produced a brilliantly
luminous flame in the arc stream which enormously increased the
efficiency of the lamp.]

[Illustration: ENCLOSED FLAME ARC LAMP, 1908.

By condensing the smoke from the arc in a cooling chamber it was
practical to enclose the flame arc, thereby increasing the life of the
carbons.]

The reason for the big difference in efficiency between the series
and multiple direct-current arc is that in the latter a large amount
of electrical energy (watts) is lost in the ballast resistance. While
there is a considerable difference between the inherent efficiencies
of the D. C. and A. C. arcs themselves, this difference is reduced in
the multiple D. C. and A. C. arc lamps as more watts are lost in the
resistance ballast of the multiple D. C. lamp than are lost in the
reactance ballast of the multiple A. C. lamp.

This reactance gives the A. C. lamp what is called a “power-factor.”
The product of the amperes (7.5) times the volts (110) does not give
the true wattage (540) of the lamp, so that the actual volt-amperes
(825) has to be multiplied by a power factor, in this case about 65
per cent, to obtain the actual power (watts) consumed. The reason
is that the instantaneous varying values of the alternating current
and pressure, if multiplied and averaged throughout the complete
alternating cycle, do not equal the average amperes (measured by an
ammeter) multiplied by the average voltage (measured by a volt-meter).
That is, the maximum value of the current flowing (amperes) does not
occur at the same instant that the maximum pressure (voltage) is on the
circuit.




THE FLAME ARC LAMP


About 1844 Bunsen investigated the effect of introducing various
chemicals in the carbon arc. Nothing was done, however, until Bremer,
a German, experimented with various salts impregnated in the carbon
electrodes. In 1898 he produced the so-called flame arc, which
consisted of carbons impregnated with calcium fluoride. This gave a
brilliant yellow light most of which came from the arc flame, and
practically none from the carbon tips. The arc operated in the open air
and produced smoke which condensed into a white powder.

The two carbons were inclined downward at about a 30-degree angle with
each other, and were of small diameter but long, 18 to 30 inches,
having a life of about 12 to 15 hours. The tips of the carbons
projected through an inverted earthenware cup, called the “economizer,”
the white powder condensing on this and acting not only as an excellent
reflector but making a dead air space above the arc. The arc was
maintained at the tips of the carbons by an electro-magnet whose
magnetic field “blew” the arc down.

Two flame arc lamps were burned in series on 110-volt circuits. They
consumed 550 watts each, giving an efficiency of about 35 lumens per
watt on direct current. On alternating current the efficiency was about
30 l-p-w. By use of barium salts impregnated in the carbons, a white
light was obtained, giving an efficiency of about 18 l-p-w on direct
current and about 15½ on alternating current. These figures cover lamps
equipped with clear glassware. Using strontium salts in the carbons,
a red light was obtained at a considerably lower efficiency, such
arcs on account of their color being used only to a limited extent for
advertising purposes.

[Illustration: CONSTANT CURRENT TRANSFORMER, 1900.

This converted alternating current of constant voltage into constant
current, for use on series circuits.]

These arcs were remarkably efficient but their maintenance expense was
high. Later, about 1908, enclosed flame arcs with vertical carbons were
made which increased the life of the carbons, the smoke being condensed
in cooling chambers. However, their maintenance expense was still high.
They have now disappeared from the market, having been displaced by the
very efficient gas-filled tungsten filament incandescent lamp which
appeared in 1913.




THE CONSTANT CURRENT TRANSFORMER FOR SERIES CIRCUITS


About 1900 the constant current transformer was developed by Elihu
Thomson. This transforms current taken from a constant potential
alternating current circuit into a constant alternating current for
series circuits, whose voltage varies with the load on the circuit.
The transformer has two separate coils; the primary being stationary
and connected to the constant potential circuit and the secondary
being movable and connected to the series circuit. The weight of the
secondary coil is slightly underbalanced by a counter weight. Current
flowing in the primary induces current in the secondary, the two coils
repelling each other. The strength of the repelling force depends
upon the amount of current flowing in the two coils. The core of the
transformer is so designed that the central part, which the two coils
surround, is magnetically more powerful close to the primary coil than
it is further away.

When the two coils are close together a higher voltage is induced in
the secondary than if the later were further away from the primary
coil. In starting, the two coils are pulled apart by hand to prevent
too large a current flowing in the series circuit. The secondary
coil is allowed to gradually fall and will come to rest at a point
where the voltage induced in it produces the normal current in the
series circuit, the repelling force between the two coils holding the
secondary at this point. Should the load in the series circuit change
for any reason, the current in the series circuit would also change,
thus changing the force repelling the two coils. The secondary would
therefore move until the current in the series circuit again becomes
normal. The action is therefore automatic, and the actual current
in the series circuit can be adjusted within limits to the desired
amount, by varying the counterweight. A dash pot is used to prevent the
secondary coil from oscillating (pumping) too much.

In the constant current transformer, the series circuit is insulated
from the constant potential circuit. This has many advantages. A
similar device, called an automatic regulating reactance was developed
which is slightly less expensive, but it does not have the advantage of
insulating the two circuits from each other.




ENCLOSED SERIES ALTERNATING CURRENT ARC LAMPS


The simplicity of the constant current transformer soon drove the
constant direct-current dynamo from the market. An enclosed arc lamp
was therefore developed for use on alternating constant current. Two
sizes of lamps were made; one for 6.6 amperes consuming 450 watts
and having an efficiency of about 4½ lumens per watt, and the other
7.5 amperes, 480 watts and 5 l-p-w (clear glassware). These lamps
soon superseded the direct current series arcs. They have now been
superseded by the more efficient magnetite arc and tungsten filament
incandescent lamps.




SERIES INCANDESCENT LAMPS ON CONSTANT CURRENT TRANSFORMERS


Series incandescent lamps were made for use on constant current
transformers superseding the “Municipal” and “Shunt Box” systems. The
large Edison, now called the Mogul Screw base, was adopted and the
short circuiting film cut-out was removed from the base and placed
between prongs attached to the socket.

[Illustration:

  Holder.      Socket.      Holder and socket.

SERIES INCANDESCENT LAMP SOCKET WITH FILM CUTOUT, 1900.

The “Large Edison,” now called Mogul Screw, base was standardized and
the short circuiting device put on the socket terminals.]

The transformers made for the two sizes of arc lamps, produced 6.6
and 7.5 amperes and incandescent lamps, in various sizes from 16 to
50 cp, were made for these currents so that the incandescent lamps
could be operated on the same circuit with the arc lamps. The carbon
series incandescent lamp, however, was more efficient if made for lower
currents, so 3½-, 4- and 5½-ampere constant current transformers were
made for incandescent lamps designed for these amperes. Later, however,
with the advent of the tungsten filament, the 6.6-ampere series
tungsten lamp was made the standard, as it was slightly more efficient
than the lower current lamps, and was made in sizes from 32 to 400 cp.
When the more efficient gas-filled tungsten lamps were developed, the
sizes were further increased; the standard 6.6-ampere lamps now made
are from 60 to 2500 cp.




THE NERNST LAMP


Dr. Walther Nernst, of Germany, investigating the rare earths used in
the Welsbach mantle, developed an electric lamp having a burner, or
“glower” as it was called, consisting of a mixture of these oxides. The
main ingredient was zirconia, and the glower operated in the open air.
It is a non-conductor when cold, so had to be heated before current
would flow through it. This was accomplished by an electric heating
coil, made of platinum wire, located just above the glower. As the
glower became heated and current flowed through it, the heater was
automatically disconnected by an electro-magnet cut-out.

[Illustration: NERNST LAMP, 1900.

The burners consisted mainly of zirconium oxide which had to be heated
before current could go through them.]

The resistance of the glower decreases with increase in current, so a
steadying resistance was put in series with it. This consisted of an
iron wire mounted in a bulb filled with hydrogen gas and was called
a “ballast.” Iron has the property of increasing in resistance with
increase in current flowing through it, this increase being very
marked between certain temperatures at which the ballast was operated.
The lamp was put on the American market in 1900 for use on 220-volt
alternating current circuits. The glower consumed 0.4 ampere. One, two,
three, four and six glower lamps were made, consuming 88, 196, 274, 392
and 528 watts respectively. As most of the light is thrown downward,
their light output was generally given in mean lower hemispherical
candlepower. The multiple glower lamps were more efficient than the
single glower, owing to the heat radiated from one glower to another.
Their efficiencies, depending on the size, were from about 3½ to 5
lumens per watt, and their average candlepower throughout life was
about 80 per cent of initial. The lamp disappeared from the market
about 1912.

[Illustration: DIAGRAM OF NERNST LAMP.]




THE COOPER-HEWITT LAMP


In 1860 Way discovered that if an electric circuit was opened between
mercury contacts a brilliant greenish colored arc was produced.
Mercury was an expensive metal and as the carbon arc seemed to give
the most desirable results, nothing further was done for many years
until Dr. Peter Cooper Hewitt, an American, began experimenting with
it. He finally produced an arc in vacuum in a one-inch glass tube
about 50 inches long for 110 volts direct current circuits, which was
commercialized in 1901. The tube hangs at about 15 degrees from the
horizontal. The lower end contains a small quantity of mercury. The
terminals are at each end of the tube, and the arc was first started
by tilting the tube by hand so that a thin stream of mercury bridged
the two terminals. Current immediately vaporized the mercury, starting
the arc. A resistance is put in series with the arc to maintain the
current constant on direct current constant voltage circuits. Automatic
starting devices were later developed, one of which consisted of an
electro-magnet that tilted the lamp, and the other of an induction coil
giving a high voltage which, in discharging, started the arc.

[Illustration: COOPER-HEWITT MERCURY VAPOR ARC LAMP, 1901.

This gives a very efficient light, practically devoid of red but of
high actinic value, so useful in photography.]

This lamp is particularly useful in photography on account of the
high actinic value of its light. Its light is very diffused and is
practically devoid of red rays, so that red objects appear black in its
light. The lamp consumes 3½ amperes at 110 volts direct current (385
watts) having an efficiency of about 12½ lumens per watt.

The mercury arc is peculiar in that it acts as an electric valve
tending to let current flow through it only in one direction. Thus
on alternating current, the current impulses will readily go through
it in one direction, but the arc will go out in the other half cycle
unless means are taken to prevent this. This is accomplished by having
two terminals at one end of the tube, which are connected to choke
coils, which in turn are connected to a single coil (auto) transformer.
The alternating current supply mains are connected to wires tapping
different parts of the coil of the auto transformer. The center of
the coil of the auto transformer is connected through an induction
coil to the other end of the tube. By this means the alternating
current impulses are sent through the tube in one direction, one half
cycle from one of the pairs of terminals of the tube, the other half
cycle from the other terminal. Thus pulsating direct current, kept
constant by the induction coil, flows through the tube, the pulsations
overlapping each other by the magnetic action of the choke coils. This
alternating current lamp is started by the high voltage discharge
method. It has a 50-inch length of tube, consuming about 400 watts on
110 volts. Its efficiency is a little less than that of the direct
current lamp.

[Illustration: DIAGRAM OF COOPER-HEWITT LAMP FOR USE ON ALTERNATING
CURRENT.

The mercury arc is inherently for use on direct current, but by means
of reactance coils, it can be operated on alternating current.]




THE LUMINOUS OR MAGNETITE ARC LAMP


About 1901 Dr. Charles P. Steinmetz, Schenectady, N. Y., studied the
effect of metallic salts in the arc flame. Dr. Willis R. Whitney,
also of Schenectady, and director of the research laboratory of the
organization of which Dr. Steinmetz is the consulting engineer,
followed with some further work along this line. The results of this
work were incorporated in a commercial lamp called the magnetite arc
lamp, through the efforts of C. A. B. Halvorson, Jr., at Lynn, Mass.
The negative electrode consists of a pulverized mixture of magnetite
(a variety of iron ore) and other substances packed tightly in an iron
tube. The positive electrode is a piece of copper sheathed in iron to
prevent oxidization of the copper. The arc flame gives a brilliant
white light, and, similar to the mercury arc, is inherently limited to
direct current. It burns in the open air at about 75 volts. The lamp is
made for 4-ampere direct current series circuits and consumes about 310
watts and has an efficiency of about 11½ lumens per watt.

[Illustration: LUMINOUS OR MAGNETITE ARC LAMP, 1902.

This has a negative electrode containing magnetite which produces a
very luminous white flame in the arc stream.]

The negative (iron tube) electrode now has a life of about 350 hours.
Later, a higher efficiency, 4-ampere electrode was made which has
a shorter life but gives an efficiency of about 17 l-p-w, and a
6.6-ampere lamp was also made giving an efficiency of about 18 l-p-w
using the regular electrode. This electrode in being consumed gives
off fumes, so the lamp has a chimney through its body to carry them
off. Some of the fumes condense, leaving a fine powder, iron oxide, in
the form of rust. The consumption of the positive (copper) electrode
is very slow, which is opposite to that of carbon arc lamps on direct
current. The arc flame is brightest near the negative (iron tube)
electrode and decreases in brilliancy and volume as it nears the
positive (copper) electrode.

[Illustration: DIAGRAM OF SERIES MAGNETITE ARC LAMP.

The method of control, entirely different from that of other arc lamps,
was invented by Halvorson to meet the peculiarities of this arc.]

The peculiarities of the arc are such that Halvorson invented an
entirely new principle of control. The electrodes are normally apart.
In starting, they are drawn together by a starting magnet with
sufficient force to dislodge the slag which forms on the negative
electrode and which becomes an insulator when cold. Current then flows
through the electrodes and through a series magnet which pulls up a
solenoid breaking the circuit through the starting magnet. This allows
the lower electrode to fall a fixed distance, about seven-eighths of
an inch, drawing the arc, whose voltage is then about 72 volts. As the
negative electrode is consumed, the length and voltage of the arc
increases when a magnet, in shunt with the arc, becomes sufficiently
energized to close the contacts in the circuit of the starting magnet
causing the electrode to pick up and start off again.




MERCURY ARC RECTIFIER FOR MAGNETITE ARC LAMPS


[Illustration: MERCURY ARC RECTIFIER TUBE FOR SERIES MAGNETITE ARC
LAMPS, 1902.

The mercury arc converted the alternating constant current into direct
current required by the magnetite lamp.]

As the magnetite arc requires direct current for its operation, the
obvious way to supply a direct constant current for series circuits
is to rectify, by means of the mercury arc, the alternating current
obtained from a constant current transformer. The terminals of the
movable secondary coil of the constant current transformer are
connected to the two arms of the rectifier tube. One end of the series
circuit is connected to the center of the secondary coil. The other
end of the series circuit is connected to a reactance which in turn
is connected to the pool of mercury in the bottom of the rectifier
tube. One-half of the cycle of the alternating current goes from the
secondary coil to one arm of the rectifier tube through the mercury
vapor, the mercury arc having already been started by a separate
starting electrode. It then goes to the pool of mercury, through
the reactance and through the series circuit. The other half cycle
of alternating current goes to the other arm of the rectifier tube,
through the mercury vapor, etc., and through the series circuit. Thus a
pulsating direct current flows through the series circuit, the magnetic
action of the reactance coil making the pulsations of current overlap
each other, which prevents the mercury arc from going out.

[Illustration: EARLY MERCURY ARC RECTIFIER INSTALLATION.]




INCANDESCENT LAMP DEVELOPMENTS, 1894–1904


With the development of a waterproof base in 1900, by the use of a
waterproof cement instead of plaster of Paris to fasten the base to
the bulb, porcelain at first and later glass being used to insulate
the terminals of the base from each other, lamps could be exposed to
the weather and give good results. Electric sign lighting therefore
received a great stimulus, and lamps as low as 2 candlepower for 110
volts were designed for this purpose. Carbon lamps with concentrated
filaments were also made for stereoptican and other focussing purposes.
These lamps were made in sizes from 20 to 100 candlepower. The arc lamp
was more desirable for larger units.

The dry battery was made in small units of 2, 3 and 5 cells, so that
lamps of about ⅛ to 1 candlepower were made for 2½, 3½ and 6½ volts,
for portable flashlights. It was not however until the tungsten
filament was developed in 1907 that these flashlights became as popular
as they now are. For ornamental lighting, lamps were supplied in round
and tubular bulbs, usually frosted to soften the light.

[Illustration: THE MOORE TUBE LIGHT, 1904.

This consisted of a tube about 1¾ inches in diameter and having a
length up to 200 feet, in which air at about one thousandth part
of atmospheric pressure was made to glow by a very high voltage
alternating current.]




THE MOORE TUBE LIGHT


Geissler, a German, discovered sixty odd years ago, that a high voltage
alternating current would cause a vacuum tube to glow. This light
was similar to that obtained by Hawksbee over two hundred years ago.
Geissler obtained his high voltage alternating current by a spark
coil, which consisted of two coils of wire mounted on an iron core.
Current from a primary battery passed through the primary coil, and
this current was rapidly interrupted by a vibrator on the principle of
an electric bell. This induced an alternating current of high voltage
in the secondary coil as this coil had a great many more turns than
the primary coil had. Scientists found that about 70 per cent of the
electrical energy put into the Geissler tube was converted into the
actual energy in the light given out.

In 1891 Mr. D. McFarlan Moore, an American, impressed with the fact
that only one-half of one per cent of the electrical energy put into
the carbon-incandescent lamp came out in the form of light, decided to
investigate the possibilities of the vacuum tube. After several years
of experiments and the making of many trial lamps, he finally, in 1904,
made a lamp that was commercially used in considerable numbers.

[Illustration: DIAGRAM OF FEEDER VALVE OF MOORE TUBE.

As the carbon terminals inside the tube absorbed the very slight
amount of gas in the tube, a feeder valve allowed gas to flow in the
tube, regulating the pressure to within one ten thousandth part of
an atmosphere above and below the normal extremely slight pressure
required.]

The first installation of this form of lamp was in a hardware store
in Newark, N. J. It consisted of a glass tube 1¾ inches in diameter
and 180 feet long. Air, at a pressure of about one-thousand part of
an atmosphere, was in the tube, from which was obtained a pale pink
color. High voltage (about 16,000 volts) alternating current was
supplied by a transformer to two carbon electrodes inside the ends of
the tube. The air had to be maintained within one ten-thousandth part
of atmospheric pressure above and below the normal of one-thousandth,
and as the rarefied air in the tube combined chemically with the carbon
electrodes, means had to be devised to maintain the air in the tube at
this slight pressure as well as within the narrow limits required.

This was accomplished by a piece of carbon through which the air could
seep, but if covered with mercury would make a tight seal. As the air
pressure became low, an increased current would flow through the tube,
the normal being about a tenth of an ampere. This accordingly increased
the current flowing through the primary coil of the transformer. In
series with the primary coil was an electro-magnet which lifted, as the
current increased, a bundle of iron wires mounted in a glass tube which
floated in mercury. The glass tube, rising, lowered the height of the
mercury, uncovering a carbon rod cemented in a tube connecting the main
tube with the open air. Thus air could seep through this carbon rod
until the proper amount was fed into the main tube. When the current
came back to normal the electro-magnet lowered the floating glass tube
which raised the height of the mercury and covered the carbon rod, thus
shutting off the further supply of air.

As there was a constant loss of about 400 watts in the transformer,
and an additional loss of about 250 watts in the two electrodes, the
total consumption of the 180-foot tube was about 2250 watts. Nitrogen
gas gave a yellow light, which was more efficient and so was later
used. On account of the fixed losses in the transformer and electrodes
the longer tubes were more efficient, though they were made in various
sizes of from 40 to 200 feet. The 200-foot tube, with nitrogen, had an
efficiency of about 10 lumens per watt. Nitrogen gas was supplied to the
tube by removing the oxygen from the air used. This was accomplished by
passing the air over phosphorous which absorbed the oxygen.

Carbon dioxide gas (CO_{2}) gave a pure white light but at about
half the efficiency of nitrogen. The gas was obtained by allowing
hydrochloric acid to come in contact with lumps of marble (calcium
carbonate) which set free carbon dioxide and water vapor. The latter
was absorbed by passing the gas through lumps of calcium chloride. The
carbon dioxide tube on account of its daylight color value, made an
excellent light under which accurate color matching could be done. A
short tube is made for this purpose and this is the only use which the
Moore tube now has, owing to the more efficient and simpler tungsten
filament incandescent lamp.




THE OSMIUM LAMP


Dr. Auer von Welsbach, the German scientist who had produced the
Welsbach gas mantle, invented an incandescent electric lamp having a
filament of the metal osmium. It was commercially introduced in Europe
in 1905 and a few were sold, but it was never marketed in this country.
It was generally made for 55 volts, two lamps to burn in series on
110-volt circuits, gave about 25 candlepower and had an initial
efficiency of about 5½ lumens per watt. It had a very fair maintenance
of candlepower during its life, having an average efficiency of about
5 l-p-w. Osmium is a very rare and expensive metal, usually found
associated with platinum, and is therefore very difficult to obtain.
Burnt out lamps were therefore bought back in order to obtain a supply
of osmium. It is also a very brittle metal, so that the lamps were
extremely fragile.

[Illustration: OSMIUM LAMP, 1905.

This incandescent lamp was used in Europe for a few years, but was
impractical to manufacture in large quantities as osmium is rarer and
more expensive than platinum.]




THE GEM LAMP


Dr. Willis R. Whitney, of Schenectady, N. Y., had invented an
electrical resistance furnace. This consisted of a hollow carbon tube,
packed in sand, through which a very heavy current could be passed.
This heated the tube to a very high temperature, the sand preventing
the tube from oxidizing, so that whatever was put inside the tube
could be heated to a very high heat. Among his various experiments,
he heated some carbon filaments and found that the high temperature
changed their resistance “characteristic” from negative to positive.
The ordinary carbon filament has a resistance when hot that is less
than when it is cold, which was reversed after heating it to the high
temperature Dr. Whitney was able to obtain. These filaments were made
into lamps for 110-volt service and it was found that they could
be operated at an efficiency of 4 lumens per watt. The lamps also
blackened less than the regular carbon lamp throughout their life.

[Illustration: GEM LAMP, 1905.

This incandescent lamp had a graphitized carbon filament obtained by
the heat of an electric furnace, so that it could be operated at 25 per
cent higher efficiency than the regular carbon lamp. This lamp is in
the exhibit of Edison lamps in the Smithsonian Institution.]

This lamp was put on the market in 1905 and was called the Gem or
metallized carbon filament lamp as such a carbon filament had a
resistance characteristic similar to metals. At first it had two single
hair pin filaments in series which in 1909 were changed to a single
loop filament like the carbon lamp.

In 1905 the rating of incandescent lamps was changed from a candlepower
to a wattage basis. The ordinary 16-candlepower carbon lamp consumed
50 watts and was so rated. The 50-watt Gem lamp gave 20 candlepower,
both candlepower ratings being their mean candlepower in a horizontal
direction. The Gem lamp was made for 110-volt circuits in sizes from
40 to 250 watts. The 50-watt size was the most popular, many millions
of which were made before the lamp disappeared from use in 1918. The
lamp was not quite as strong as the carbon lamp. Some Gem lamps for
series circuits were also made, but these were soon superseded by the
tungsten-filament lamp which appeared in 1907.




THE TANTALUM LAMP


[Illustration: TANTALUM LAMP, 1906.

The tantalum filament could be operated at 50 per cent greater
efficiency than that of the regular carbon incandescent lamp. This lamp
is in the exhibit of Edison lamps in the Smithsonian Institution.]

Dr. Werner von Bolton, a German physicist, made an investigation of
various materials to see if any of them were more suitable than carbon
for an incandescent-lamp filament. After experimenting with various
metals, tantalum was tried. Tantalum had been known to science for
about a hundred years. Von Bolton finally obtained some of the pure
metal and found it to be ductile so that it could be drawn out into a
wire. As it had a low specific resistance, the wire filament had to
be much longer and thinner than the carbon filament. A great number
of experimental lamps were made so that it was not until 1906 that
the lamp was put on the market in this country. It had an initial
efficiency of 5 lumens per watt and a good maintenance of candle power
throughout its life, having an average efficiency of about 4¼ l-p-w.
The usual sizes of lamps were 40 and 80 watts giving about 20 and 40
candlepower respectively. It was not quite as strong as the carbon
lamp, and on alternating current the wire crystallized more rapidly,
so that it broke more easily, giving a shorter life than on direct
current. It disappeared from use in 1913.




INVENTION OF THE TUNGSTEN LAMP


Alexander Just and Franz Hanaman in 1902 were laboratory assistants
to the Professor of Chemistry in the Technical High School in Vienna.
Just was spending his spare time in another laboratory in Vienna,
attempting to develop a boron incandescent lamp. In August of that year
he engaged Hanaman to aid him in his work. They conceived the idea of
making a lamp with a filament of tungsten and for two years worked on
both lamps. The boron lamp turned out to be a failure. Their means
were limited; Hanaman’s total income was $44 per month and Just’s was
slightly more than this. In 1903 they took out a German patent on a
tungsten filament, but the process they described was a failure because
it produced a filament containing both carbon and tungsten. The carbon
readily evaporated and quickly blackened the bulb when they attempted
to operate the filament at an efficiency higher than that possible with
the ordinary carbon filament. Finally in the latter part of the next
year (1904) they were able to get rid of the carbon and produced a pure
tungsten filament.

Tungsten had been known to chemists for many years by its compounds,
its oxides and its alloys with steel, but the properties of the pure
metal were practically unknown. It is an extremely hard and brittle
metal and it was impossible at that time to draw it into a wire. Just
and Hanaman’s process of making a pure tungsten filament consisted of
taking tungsten oxide in the form of an extremely fine powder, reducing
this to pure tungsten powder by heating it while hydrogen gas passed
over it. The gas combined with the oxygen of the oxide, forming water
vapor which was carried off, leaving the tungsten behind.

The tungsten powder was mixed with an organic binding material, and
the paste was forced by very high pressure through a hole drilled in
a diamond. This diamond die was necessary because tungsten, being so
hard a substance, would quickly wear away any other kind of die. The
thread formed was cut into proper lengths, bent the shape of a hair
pin and the ends fastened to clamps. Current was passed through the
hair pin in the presence of hydrogen gas and water vapor. The current
heated the hair pin, carbonized the organic binding material in it, the
carbon then combining with the moist hydrogen gas, leaving the tungsten
particles behind. These particles were sintered together by the heat,
forming the tungsten filament. Patents were applied for in various
countries, the one in the United States on July 6, 1905.

The two laboratory assistants in 1905 finally succeeded in getting
their invention taken up by a Hungarian lamp manufacturer. By the end
of the year lamps were made that were a striking success for they could
be operated at an efficiency of 8 lumens per watt. They were put on
the American market in 1907, the first lamp put out being the 100-watt
size for 110-volt circuits. This was done by mounting several hair pin
loops in series to get the requisite resistance, tungsten having a
low specific resistance. The issue of the American patent was delayed
owing to an interference between four different parties, each claiming
to be the inventor. After prolonged hearings, one application having
been found to be fraudulent, the patent was finally granted to Just and
Hanaman on February 27, 1912.

[Illustration: TUNGSTEN LAMP, 1907.

The original 100 watt tungsten lamp was nearly three times as efficient
as the carbon lamp, but its “pressed” filament was very fragile. This
lamp is in the exhibit of Edison lamps in the Smithsonian Institution.]

This “pressed” tungsten filament was quite fragile, but on account of
its relatively high efficiency compared with other incandescent lamps,
it immediately became popular. Soon after its introduction it became
possible to make finer filaments so that lamps for 60, 40 and then 25
watts for 110-volt circuits were made available. Sizes up to 500 watts
were also made which soon began to displace the enclosed carbon arc
lamp. Lamps were also made for series circuits in sizes from 32 to 400
candlepower. These promptly displaced the carbon and Gem series lamps.
The high efficiency of the tungsten filament was a great stimulus to
flashlights which are now sold by the millions each year. The lighting
of railroad cars, Pullmans and coaches, with tungsten lamps obtaining
their current from storage batteries, soon superseded the gas light
formerly used. In some cases, a dynamo, run by a belt from the car
axle, kept these batteries charged.

[Illustration: DRAWN TUNGSTEN WIRE LAMP, 1911.

Scientists had declared it impossible to change tungsten from a brittle
to ductile metal. This, however, was accomplished by Dr. Coolidge, and
drawn tungsten wire made the lamp very sturdy. This lamp is in the
exhibit of Edison lamps in the Smithsonian Institution.]




DRAWN TUNGSTEN WIRE


After several years of patient experiment, Dr. William D. Coolidge
in the research laboratory of a large electrical manufacturing
company at Schenectady, N. Y., invented a process for making tungsten
ductile, a patent for which was obtained in December, 1913. Tungsten
had heretofore been known as a very brittle metal, but by means of
this process it became possible to draw it into wire. This greatly
simplified the manufacture of lamps and enormously improved their
strength. Such lamps were commercially introduced in 1911.

With drawn tungsten wire it was easier to coil and therefore
concentrate the filament as required by focusing types of lamps. The
automobile headlight lamp was among the first of these, which in 1912
started the commercial use of electric light on cars in place of oil
and acetylene gas. On street railway cars the use of tungsten lamps,
made possible on this severe service by the greater sturdiness of
the drawn wire, greatly improved their lighting. Furthermore, as the
voltage on street railway systems is subject to great changes, the
candlepower of the tungsten filament has the advantage of varying but
about half as much as that of the carbon lamp on fluctuating voltage.

[Illustration: QUARTZ MERCURY VAPOR LAMP, 1912.

The mercury arc if enclosed in quartz glass can be operated at much
higher temperature and therefore greater efficiency. The light is
still deficient in red but gives a considerable amount of ultra-violet
rays which kill bacteria and are very dangerous to the eye. They can,
however, be absorbed by a glass globe. The lamp is not used as an
illuminant in this country, but is valuable for use in the purification
of water.]




THE QUARTZ MERCURY VAPOR ARC LAMP


By putting a mercury arc in a tube made of quartz instead of glass,
it can be operated at a much higher temperature and thereby obtain a
greater efficiency. Such a lamp, however, is still largely deficient in
red rays, and it gives out a considerable amount of ultra-violet rays.
These ultra-violet rays will kill bacteria and the lamp is being used
to a certain extent for such purpose as in the purification of water.
These rays are very dangerous to the eyes, but they are absorbed by
glass, so as an illuminant, a glass globe must be used on the lamp.
These lamps appeared in Europe about 1912 but were never used to any
extent in this country as an illuminant. They have an efficiency of
about 26 lumens per watt. Quartz is very difficult to work, so the cost
of a quartz tube is very great. The ordinary bunsen gas flame is used
with glass, but quartz will only become soft in an oxy-hydrogen or
oxy-acetylene flame.

[Illustration: GAS FILLED TUNGSTEN LAMP, 1913.

By operating a coiled filament in an inert gas, Dr. Langmuir was able
to greatly increase its efficiency, the gain in light by the higher
temperature permissible, more than offsetting the loss of heat by
convection of the gas. This lamp is in the exhibit of Edison lamps in
the Smithsonian Institution.]




THE GAS-FILLED TUNGSTEN LAMP


The higher the temperature at which an incandescent lamp filament can
be operated, the more efficient it becomes. The limit in temperature is
reached when the material begins to evaporate rapidly, which blackens
the bulb. The filament becoming thinner more quickly, thus rupturing
sooner, shortens the life. If, therefore, the evaporating temperature
can by some means be slightly raised, the efficiency will be greatly
improved. This was accomplished by Dr. Irving Langmuir in the research
laboratories at Schenectady, N. Y., by operating a tungsten filament
in an inert gas. Nitrogen was first used. The gas circulating in the
bulb has the disadvantage of conducting heat away from the filament
so that the filament was coiled. This presented a smaller surface to
the currents of gas and thereby reduced this loss. The lamps were
commercially introduced in 1913 and a patent was granted in April, 1916.

[Illustration: GAS FILLED TUNGSTEN LAMP, 1923.

This is the form of the lamp as at present made. For 110-volt circuits
the sizes range from 50 to 1000 watts.]

An increased amount of electrical energy is required in these lamps
to offset the heat being conducted away by the gas. This heat loss is
minimized in a vacuum lamp, the filament tending to stay hot on the
principle of the vacuum bottle. This loss in a gas filled lamp becomes
relatively great in a filament of small diameter, as the surface in
proportion to the volume of the filament increases with decreasing
diameters. Hence there is a point where the gain in temperature is
offset by the heat loss. The first lamps made were of 750 and 1000
watts for 110-volt circuits. Later 500- and then 400-watt lamps were
made. The use of argon gas, which has a poorer heat conductivity than
nitrogen, made it possible to produce smaller lamps, 50-watt gas-filled
lamps for 110-volt circuits now being the smallest available. In the
present state of the art, a vacuum lamp is more efficient than a
gas-filled lamp having a filament smaller than one consuming about half
an ampere. Thus gas-filled lamps are not now practicable much below 100
watts for 220 volts, 50 watts for 110 volts, 25 watts for 60 volts, 15
watts for 30 volts, etc.

From the foregoing it will be seen that the efficiency of these lamps
depends largely on the diameter of the filament. There are other
considerations, which also apply to vacuum lamps, that affect the
efficiency. Some of these are: the number of anchors used, as they
conduct heat away; in very low voltage lamps having short filaments the
relative amount of heat conducted away by the leading-in wires becomes
of increasing importance, etc. The 1000-watt lamp for 110-volt circuits
is now made for nearly 20½ lumens per watt; the 50-watt lamp a little
over 10 l-p-w.

The advent of the tungsten filament and especially the gas-filled
lamp sounded the doom of all other electric illuminants except the
magnetite and mercury arc lamps. All other incandescent lamps have now
practically disappeared. The flame arc as well as the enclosed carbon
arc lamp are hardly ever seen. The simplicity of the incandescent
lamp, its cleanliness, low first cost, low maintenance cost and high
efficiency of the tungsten filament have been the main reasons for its
popularity.




TYPES AND SIZES OF TUNGSTEN LAMPS NOW MADE


There are about two hundred different types and sizes of tungsten
filament lamps now standard for various kinds of lighting service. For
110-volt service, lamps are made in sizes from 10 to 1000 watts. Of
the smaller sizes, some are made in round and tubular-shaped bulbs for
ornamental lighting. In addition there are the candelabra lamps used
in ornamental fixtures. Twenty-five- to five hundred-watt lamps are
made with bulbs of special blue glass to cut out the excess of red and
yellow rays and thus produce a light approximating daylight.

For 220-volt service lamps are made in sizes of from 25 to 1000 watts.
For sign lighting service, 5-watt lamps of low voltage are made for
use on a transformer located near the sign to reduce the 110 volts
alternating current to that required by the lamps. Lamps are made from
5 to 100 watts for 30-volt service, such as is found in train lighting
and in gas engine driven dynamo sets used in rural homes beyond the
reach of central station systems. Concentrated filament lamps are
made for stereopticon and motion picture projection, floodlighting,
etc., in sizes from 100 to 1000 watts, for street railway headlights
in sizes below 100 watts and for locomotive headlights in sizes from
100 to 250 watts. For series circuits, used in street lighting, lamps
are made from 60 to 2500 candlepower. Miniature lamps cover those for
flashlight, automobile, Christmas-tree, surgical and dental services,
etc. They range, depending on the service, from ½ to 21 candlepower,
and in voltage from 2½ to 24.

[Illustration: STANDARD TUNGSTEN LAMPS, 1923.

This illustrates some of the two hundred different lamps regularly
made.]




STANDARD VOLTAGES


Mention has been made of 110-volt service, 220-volt service, etc.
In the days of the carbon incandescent lamp it was impossible to
manufacture all lamps for an exact predetermined voltage. The popular
voltage was 110, so lighting companies were requested in a number of
instances to adjust their service to some voltage other than 110. They
were thus able to utilize the odd voltage lamps manufactured, and this
produced a demand for lamps of various voltages from 100 to 130. Arc
lamps had a resistance (reactance on alternating current) that was
adjustable for voltages between 100 and 130.

Similarly a demand was created for lamps of individual voltages of
from 200 to 260. The 200- to 260-volt range has simmered down to
220, 230, 240 and 250 volts. These lamps are not as efficient as the
110-volt type and their demand is considerably less, as the 110-volt
class of service for lighting is, with the exception of England,
almost universal. Thus 110-volt service means 100 to 130 volts in
contra-distinction to 200 to 260 volts, etc. The drawn tungsten wire
filament made it possible to accurately predetermine the voltage of
the lamp, so now that the carbon incandescent lamp is a thing of the
past, there is no need for so many different voltages. Several years
ago standard voltages of 110, 115 and 120 were recommended for adoption
by all the electrical societies in the United States, and practically
all central stations have now changed their service to one of these
voltages.




COST OF INCANDESCENT ELECTRIC LIGHT


In the early ’80’s current was expensive, costing a consumer on the
average about twenty cents per kilowatt hour. The cost has gradually
come down and the general average rate for which current is sold for
lighting purposes is now about 4½ cents. During the period 1880 to 1905
the average efficiency of carbon lamps throughout their life increased
from about one to over 2¾ lumens per watt and their list price
decreased from one dollar to twenty cents. The average amount of light
obtained for one cent at first was about five candlepower hours and in
1904 it was increased to over thirty-six at the average rate then in
effect. The next year with the more efficient Gem lamp 44 candle-hours
could be had for one cent. In 1906 the amount was increased to 50 with
the tantalum lamp and with the tungsten lamp in 1907, even at its high
price of $1.50, the amount was further increased to 63. Since then
the average cost of current has been reduced but slightly, but the
efficiency of the tungsten lamp has materially increased and its cost
reduced so that it is now possible to obtain, with the ordinary 40-watt
lamp 170 candle-hours for a cent. If the gas-filled tungsten lamp were
used the amount of light now obtained for a cent would depend upon the
size, which, for the 1000-watt lamp, would be 382 candle-hours.




STATISTICS REGARDING THE PRESENT DEMAND FOR LAMPS


In the United States there are about 350 million incandescent and
about two hundred thousand magnetite arc lamps now (1923) in use.
They are increasing about 10 per cent each year. The annual demand
for incandescent lamps for renewals and new installations is over 200
millions, exclusive of miniature lamps. The use of incandescent lamps
in all other countries put together is about equal that in the U. S.

The average candlepower of standard lighting lamps has increased from
16, which prevailed during the period prior to 1905, to over 60. The
average wattage has not varied much during the past twenty-odd years,
the average lamp now consuming about 55 watts. This indicates that the
public is utilizing the improvement in lamp efficiency by increased
illumination. The present most popular lamp is the 40-watt size which
represents 20 per cent of the total demand. Second in demand is the
25-watt at 18 per cent and third, the 50-watt at 15 per cent of the
total in numbers. While the aggregate demand of all the gas-filled
tungsten lamps is a little over 20 per cent in numbers, they represent,
on account of their greater efficiency and wattage, over half the
amount of total candlepower used. In the United States about 85 per
cent of all lamps are for the 110-volt range. About 5 per cent for 220
volts, 2 per cent for street series lighting, 3 per cent for street
railway and 5 per cent for trainlighting and miscellaneous classes of
service.




SELECTED BIBLIOGRAPHY


  ALGLAVE AND BOULARD, “The Electric Light,” translated by T.
      O’Connor Sloane, edited by C. M. Lungren, D. Appleton & Co.,
      New York, 1884.

  BARHAM, G. BASIL, “The Development of the Incandescent Electric
      Lamp,” Scott Greenwood & Son, London, 1912.

  DREDGE, JAMES, “Electric Illumination,” 2 vols., John Wiley & Sons,
      New York, 1882.

  DURGIN, WILLIAM A., “Electricity--Its History and Development,”
      A. C. McClurg & Co., Chicago, 1912.

  DYER & MARTIN, “Edison, His Life and Inventions,” 2 vols., Harper &
      Bros., New York, 1910.

  GUILLEMIN, AMEDEE, “Electricity and Magnetism,” edited by Silvanus
      P. Thompson, McMillan & Co., London, 1891.

  HOUSTON, EDWIN J., “Electricity One Hundred Years ago and To-day,”
      The W. J. Johnston Co., New York, 1894.

  HOUSTON AND KENNELLY, “Electric Arc Lighting,” McGraw Publishing
      Co., New York, 1906.

  HUTCHINSON, ROLLIN W., JR., “High Efficiency Electrical Illuminants
      and Illumination,” John Wiley & Sons, New York, 1911.

  MAIER, JULIUS, “Arc and Glow Lamps,” Whittaker & Co., London, 1886.

  POPE, FRANKLIN LEONARD, “Evolution of the Electric Incandescent
      Lamp,” Boschen & Wefer, New York, 1894.

  SOLOMON, MAURICE, “Electric Lamps,” D. Van Nostrand Co., New York,
      1908.




Transcriber’s Notes


Punctuation, hyphenation, and spelling were made consistent when a
predominant preference was found in the original book; otherwise they
were not changed.

Simple typographical errors were corrected; unbalanced quotation
marks were remedied when the change was obvious, and otherwise left
unbalanced.

Illustrations in this eBook have been positioned between paragraphs. In
versions of this eBook that support hyperlinks, the page references in
the List of Illustrations lead to the corresponding illustrations.

“Allesandro Volta” was printed that way.