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Catalog A. 1908.

ASTRONOMICAL INSTRUMENTS
... AND ...
ACCESSORIES.

[Illustration]

WM. GAERTNER & CO.
5345-5349 Lake Ave.
CHICAGO.




Catalog A. 1908.

ASTRONOMICAL INSTRUMENTS
... AND ...
ACCESSORIES.

[Illustration]

WM. GAERTNER & CO.
5345-5349 Lake Ave.
CHICAGO.




Notice.


This catalogue supersedes former editions.

The prices given in this catalogue are net and do not include packing which
will be charged at cost.

To avoid mistakes and delays when ordering please give catalogue number and
shipping instructions.

Most of the instruments listed in this catalogue are constructed to order
only but the smaller sizes of telescopes with accessories, chronographs,
simpler measuring machines, etc., are usually kept in stock.

The apparatus listed in this catalogue is of our own manufacture, excepting
the astronomical regulator clocks, which we have listed for the convenience
of our customers.

All orders will be filled as promptly as possible with due regard to
thorough workmanship and efficient inspection.

Everything that leaves our establishment is carefully tested and inspected
and we can guarantee our apparatus to be, in every respect, fully as
represented. Any piece, which does not come up to the most exacting
requirements will always be promptly replaced within the shortest possible
time.

We shall be glad to satisfy any special requirements of our customers and
will make any desired alterations and additions on the standard designs.




Introduction.


In the following pages we have endeavored to give to our customers an idea
of the line of astronomical instruments of the latest and most improved
types which we have constructed for some of the leading observatories as
mentioned in the text. We feel that this series of illustrations may not
only be of general interest, but also of service in helping to determine
further developments of modern astronomical and astrophysical equipment. We
have not thought it advisable to describe in detail the various instruments
of precision, which we have been called upon to construct from time to time
for the scientists in the astronomical as well as other branches of science
during the last ten years. As a rule every astronomer is interested in some
special line of research, which for a successful investigation requires a
special adaptation of the instrument he proposes to use, and in such cases
we are confident we can fill the requirements and shall be happy to
correspond with interested parties. We are in position to undertake the
design of special apparatus and can furnish sketches and estimates in
accordance with the suggestions of the customer on short notice in such
cases, where the importance of the prospective business will warrant it.
Among the various instruments which we have built, but which are not
included in this catalogue, we wish to mention, spectroheliographs,
planetary cameras, photographic plate holders, domes for observatories,
etc.

The optical parts which we furnish are of the highest degree of excellence
and are made for us by several of the most reliable firms in this line.

Mr. O. L. Petitdidier is closely located to our works, and during the last
ten years has supplied most of our objectives, etc.

It is and has been the aim of our firm to produce apparatus of the highest
grade and the constant growth of our business is a mute but eloquent
testimonial that our efforts have been appreciated by our customers.

We are glad to acknowledge our indebtedness to many of the foremost
astronomers, who have greatly assisted us by suggestions as to their
particular requirements, and by supplying certain of the photographs here
reproduced.

We take this opportunity to thank our customers for the favors rendered us
in the past, and trust that in the future these mutually pleasant relations
may be renewed.

[Illustration: A 101]

#A101. Alt-Azimuth Mounting# on strong hardwood tripod. The vertical and
horizontal axis have large bearing surfaces, assuring stability and
steadiness of motion. All parts excepting the tripod head are made of brass
and are nicely finished. The telescope is fitted with long rack and pinion
motion. Three celestial eye pieces are included. Price with 2½"
telescope                                                          #$90.00#

#A102.# The same as above with 3" telescope. Price                #$110.00#

#A103.# The same as above with 3½" telescope. Price               #$140.00#

#A104.# The same as above with 4" telescope. Price                #$200.00#

#Note.#--All our astronomical telescope have objectives of the standard
focal length (focus = to about 15 times diameter of aperture). The
objective is mounted in the most approved manner and is provided with
adjustment for collimation.

#Note.#--For accessories to these telescopes see page 11.

[Illustration: A 110]

#A110. Universal Equatorial Mounting.# This form of mounting can be used
equally well for celestial and terrestrial observations. The mounting is
made to swivel on the tripod head, in order to set the instrument in the
meridian. The polar axis can be set at any latitude and a graduated arc
gives the exact position. The instrument is set level by means of two small
levels attached to the tripod top. The polar axis is fitted with worm wheel
and worm for slow motion. The handle with the universal joint can be
clamped on either side of the worm shaft. Telescope of 3" aperture and
three eye pieces. Price                                           #$165.00#

#A111.# Same as above with 3½" telescope. Price                   #$190.00#

#A112.# Same as above with 4" telescope. Price                    #$250.00#

For accessories see page 11.

[Illustration: A 120]

#A120. Portable Equatorial Mounting with Driving Clock.# This instrument
was designed to meet the demand for portable low priced telescope suitable
for the study of astronomy in the college, high school or for the amateur
astronomer. Every observer and teacher in astronomy will appreciate the
great usefulness of a driving mechanism, which will keep the star in the
field during observation. After several years of experimenting we have
succeeded in constructing a reliable clock which can easily be attached to
our portable telescope mounting.

The instrument is mounted on strong hardwood tripod fitted with iron shoes.
It is attached to the tripod top by a single screw which holds it firmly
and allows adjustment in azimuth. The clock case carrying the bearing for
the polar axis is made to swivel in the base casting, so that the polar
axis may be easily set and firmly clamped at an angle from horizontal to
vertical. A level is fitted to the tripod top and a graduated arc is
fastened to the clock case. If the polar axis is set vertical and the worm
wheel unclamped, the instrument is transformed into an alt-azimuth
mounting. This feature will be found to be a great convenience especially
for terrestrial observations.

Both the polar and declination axes are carefully fitted to their bearings
and carry finding circles. The right ascension circle reads to 5 min., the
declination circle to single degrees. The declination axis is fitted with
clamp screw which is within convenient reach.

The clock has ample power and is enclosed in a heavy case which protects it
from dust and injury. It is driven by two strong springs and will run about
12 hours without rewinding. A lever for starting or stopping is provided.
Motion from clock to polar axis is transmitted by means of a set of bevel
gears and worm and worm wheel. The worm wheel is held by friction to the
polar axis so that the telescope can be moved without loosening any screw
and without affecting the clock. The clock will give steady and accurate
motion to the telescope and with ordinary care it will keep in good repair
for years. A slow motion adjustment independent of the clock is fitted to
the polar axis.

With the instrument are furnished three celestial eye pieces giving a
magnifying power of about 50, 100 and 150 diameters respectively.

The instrument is easily portable, the total weight of a 3" telescope being
about 60 lbs. yet it is made heavy enough, and the material well
distributed to insure strength and steadiness. Workmanship and finish of
the instrument are the best. The brass parts are either lacquered yellow or
bronzed. The iron parts are durably enameled and all exposed steel parts
are nickel-plated.

#A120.# Telescope of 3" aperture. Price                           #$190.00#

#A121.# Telescope of 3½" aperture, the same as above but the bearing parts
made proportionally heavier. Price                                #$240.00#

#A122.# Telescope of 4" aperture. Price                           #$320.00#

For accessories see page 11.

#Note.#--An iron column can be provided for above telescopes in place of of
the tripod, at an extra cost of $20.00.

[Illustration: A 130]




EQUATORIAL MOUNTINGS ON IRON PILLAR WITH DRIVING CLOCK, ETC.


On page 10 is shown an illustration of our standard high grade type of 6
in. equatorial. A description of the same will apply to practically all
larger and smaller sizes.

The pillar is of rectangular cross section and well proportioned. The clock
case is securely fastened to the top of the pillar but with provision for
adjustment in azimuth. The clock has ample driving power, is very carefully
constructed and regulated by friction governor (Design Prof. Young.)
Maintaining gears are provided on the main shaft which allows the winding
of the clock without retarding motion. Worm wheel and worm are carefully
cut, and protected by brass shields. Right ascension and declination
circles have fine graduation on solid silver and coarse finding graduation
on the edge. Electric illumination and magnifying glasses are fitted to the
verniers. The handles for all clamps and slow motions are fastened
conveniently near the eye end of the telescope and are of different shape
so as to distinguish in the dark right ascension and declination. The axes
are of tool steel carefully fitted to their bearings, and on the larger
instruments friction rollers are fitted to the polar axis. The telescope
tube is made of steel, light but strongly constructed. The eye end has long
and heavy rack and pinion motion and the whole can be easily removed.

#Note.#--The fine divided circles are often omitted on smaller equatorials,
as they are not essential, the electrical illumination for the circles is
also left off, and this will amount to a material saving.

#A130. Equatorial Mounting with 5 in. Telescope.# According to above
description with first class objective, and five eye pieces.
Price                                                             #$950.00#

The same instrument without fine circles and electrical illumination.
Price                                                             #$825.00#

#A131. Equatorial Mounting with 6 in. Telescope.#
Complete as A130. Price                                          #$1500.00#

#A132. Equatorial Mounting with 8 in. Telescope.#
Same as above. Price                                             #$2500.00#

#A133. Equatorial Mounting with 9 in. Telescope.#
Same as above. Price                                             #$3300.00#

#A134. Equatorial Mounting with 10 in. Telescope.#
Same as above. Price                                             #$3700.00#

#A135. Equatorial Mounting with 12 in. Telescope.#
Same as above. Price                                             #$5500.00#

#Note.#--We are equipped to construct larger instruments and are glad to
give prices on application.

[Illustration: A 131]

[Illustration]

The above cut shows a driving clock for our standard 6 in. telescope.

We have constructed clocks for a number of larger telescopes among others
the clock for the 24 in. Lowell Refractor.




ACCESSORIES TO TELESCOPES A101 TO A135.

#A140. Finder# fitted to 3" telescope. Price                       #$12.00#

#A141. Finder# fitted to 3½" telescope. Price                      #$15.00#

#A150. Positive Eye Pieces.# (Ramsden), focus 6 mm. to 25 mm.
Price                                                               #$4.50#

#A151. Negative Eye Pieces.# (Huygenian), focus 5 mm. to 25 mm.
Price                                                               #$4.50#

#A152. Diagonal Eye Piece.# The prism of the eye piece has guaranteed
optically plane surfaces and will not affect the definition of the
telescope. Price                                                   #$12.00#

#A153. Terrestrial Eye Piece#, focus 25 mm. Price                  #$12.00#

#A154. Sun Caps#, to fit above eye pieces. Price                    #$1.50#

The outside diameter of all our eye pieces is 1¼" excepting those used in
our Micrometers.

[Illustration: A 201]

#A201. Position Micrometers for 6" to 8" Telescopes.# Circle 15 cm.
diameter, divisions on solid silver, verniers reading to 6 min., slow gear
motion for rotating, electrical illumination, provided with different color
screens. Screw guaranteed of highest accuracy. Price              #$200.00#

#A202. Position Micrometers for 4" to 5" Telescopes.# Similar to above but
rotation by hand and construction somewhat simpler. Price         #$100.00#

[Illustration: A 203]

#A203. Small Position Micrometer for 3" to 4" Telescopes.# Circle reads
to single degrees. Electric illumination. Price                    #$75.00#

[Illustration: A 301]

#Transit Instrument#, with reversing arrangement, illumination with oil or
electric lamp, Filar micrometer with two eye pieces. Weight of axis
balanced by springs and rollers. The circle has a diameter of 150 mm.,
verniers read to 20 seconds. The instrument is mounted on an iron base
plate, which is fitted with azimuth adjustment (not shown in cut).

#A301. Transit# with 2" Telescope. Price                          #$550.00#

#A302. Transit# with 3" Telescope. Price                          #$800.00#

[Illustration: A 401]

#A401. Universal Instrument.# Telescope with objective prism. Vertical
circle has a diameter of 13 cm. is divided to 10 min. and reads by means of
two micrometer microscopes to 10 sec. The telescope is fitted with hard
phosphor bronze bearing rings and is reversible. Aperture of objective is
30 mm. Two eye pieces are furnished giving magnification of 20 and 30
diameters. The prism has absolutely plane surfaces and will not affect the
definition. Striding level reads to 2 sec. The horizontal circle is
protected and reads by means of two verniers to 1 min. The instrument is
packed in a light but strong case. Price complete with tripod     #$420.00#

#Note.#--This instrument was first constructed for Mr. E. de K.
Leffingwell, who has found it very satisfactory for his work in the polar
regions.

[Illustration: A 501]

#A501. Zoellner Astrophotometer.# The instrument is made to attach to the
eye end of the telescope and may be used with any size of refractor or
reflector. An axis parallel to the telescope tube allows the instrument to
rotate as a whole. A clamp is provided to hold it in position. The
artificial star is formed by a small incandescent lamp which is adjustable
in any direction, and in front of which is mounted a small diaphragm. The
color changing device, consisting of Nicol prism and quartz plate, is
fitted with a divided circle reading to single degrees. The circle
revolving with the Nicol prism for changing the intensity of the star, has
a diameter of 14 cm. and reads by means of two verniers to 6 min. A concave
lens is mounted in the path of the artificial star to make the light
diverging at the proper angle and a plane parallel plate is adjustably
fixed in the center of the box in order to throw the light in the eye
piece. An achromatic objective in front of the eye piece brings the images
of the real and artificial star to a focus in the same plane.
Price                                                             #$150.00#

[Illustration: A 601]

[Illustration: A 602]

#A601. Small Spectroscope.# Suitable for telescope from 3 to 6 in.
aperture. The collimator and observing telescope have an aperture of 25
mm., focus of 200 mm. Both are fitted with rack and pinion. The
spectroscope may be used with a grating or a 60 degree prism, and for this
purpose has openings for the telescopes at the proper angles. A position
circle of 75 mm. diameter, reading to degrees, is fitted to the instrument.
The slit has micrometer head.

Price, without grating, but including 60 degree prism              #$75.00#

#Note.#--This spectroscope can also be used on a support for laboratory
work.

#Support# for above spectroscope. Price                             #$4.50#

#A602. Spectroscope# for telescopes from 6 in. to 18 in. aperture and
detailed description on application.

[Illustration: A 701]

#A701. Chronograph# for physical and astronomical work. This chronograph is
designed to meet the demand for a medium sized, well-made and accurate
instrument of this kind and has given very good satisfaction. The cylinder
is 15 cm. in diameter 25 cm. long, driven by strong, carefully made clock
work, fitted with friction governor. Two different speeds for the cylinder
can be obtained by means of change gears. The slow speed of the drum is one
revolution per minute, and at this speed the drum will run for a full hour.
The fast speed is 30 seconds per revolution. The carriage is driven by
means of a screw, the nut of which is made to disengage easily.

Price of the instrument complete with two pens and glass cover    #$225.00#

#A701a. Chronograph#, the same as A701 but with only one pen. The carriage
is so constructed that a second pen can easily be added later. Price with
glass cover                                                       #$195.00#

#Note.#--Every instrument is carefully tested before being sent out and we
can guarantee the speed not to vary over 1-20 second during the full run of
one hour. Large temperature changes will not affect the speed of the clock.
A large number of the chronographs are in use and have given excellent
satisfaction.

[Illustration: A 702]

#A702. Prof. G. W. Hough's Printing Chronograph.# The instrument consists
of two carefully and accurately constructed clock movements, which are
driven by gravity and controlled electrically by the sidereal clock. The
movements revolve three type wheels. One of these turns once per second,
its edge is divided in 50 parts and it is driven by a separate movement.
The second wheel turns once per minute and the third once per hour and they
will print the seconds and minutes, while the first will give the
hundredths of seconds. A strip of paper is carried over these wheels and
moved forward by the same electro-magnet, which operates the printing
hammers. The paper is sufficiently long for 1200 observations including
spacing between records. The operation of the printing hammers is such that
the uniform motion of the type wheel is not disturbed in the act of
printing. The whole instrument is mounted on a heavy slate plate 45 cm. by
60 cm., and protected by a glass cover.

The manipulation of the apparatus is extremely simple and convenient and
the records obtained are perfectly reliable and accurate within about 0.01
of a second. The saving of time and labor by the printing chronograph is
very considerable and the filing of the records very convenient.

This printing chronograph has been in use at the Dearborn Observatory for
about twenty years and during the last five years the following
observatories have been equipped with the instrument: Amherst College
Observatory; Case School of Applied Science, Cleveland; Philadelphia
Observatory; Durham Observatory, Durham, England; Observatory of LaPlatta,
Argentine; and Dominion Observatory, Ottawa, Canada.

Prof. Hough has kindly consented to inspect every chronograph before it
leaves our shop. Price, complete on stand, glass cover, etc.      #$500.00#

[Illustration: A 801]

[Illustration: A 802]

#A801. Laboratory Clock.# This is an eight-day clock; has a movement of the
best workmanship, is driven by two strong springs, and keeps accurate time.
The dial is 12 inches in diameter and has hour, minute and second hands.
Pendulum beats seconds and makes electric contact by means of an adjustable
mercury cup. It is mounted in a hardwood case with glass door.
Price                                                              #$27.00#

#A802. Laboratory Clock.# The same as preceding one, but with better clock
movement, gravity driven. Price                                    #$35.00#

#A803. Regulator Clock.# This clock has a first-class eight day movement
with cut steel pinions. It is fitted with mercury compensation pendulum and
electrical seconds contact. Price                                 #$200.00#

#Note.#--We can furnish free of duty to educational institutions
astronomical precision clocks made by C. Riefler, Germany, and will be
pleased to quote prices to interested parties.

[Illustration: A 1200]

#A1200. Simple Comparator.# (Fig. A1200.) Built up of #Micrometer Slide#
M301 and #Microscope# M101, #with support# M310 #Fitted with Stage#. The
stage is 150 mm. long and provided with clips for holding objects, such as
spectrum photographs, scales, etc., and is fitted with illuminating mirror.
Price                                                              #$45.00#

#A1201. Small Comparator.# The instrument is intended for measuring spectra
photographs, gratings, divided scales, or such objects which can be focused
by the microscope and will allow rapid measurements of the highest possible
accuracy. The measurement depends on the accuracy of the micrometer screw,
which is cut and corrected with great care. The screw has a pitch of .5 mm.
and diameter of 15 mm. The index head attached to the screw is of
considerable diameter so as to allow the direct reading of .001 mm. The
head is divided on solid silver in 500 parts, and carries two rows of
figures indicating the first and second half of the mm. The full mm. are
read by means of a scale in front of the instrument. The bed plate is
heavy, of cast iron, and the guides are carefully scraped true within 0.001
mm. The carriage has a movement of 80 mm., is made of gun metal and fitted
exactly to the guides; it is also provided with a second or top carriage
with 40 mm. motion. The top carriage can be moved by hand and accurately
set by means of a micrometer screw. The microscope is of variable
magnifying power, focused by rack and pinion. Illumination for transparent
objects is given from below by means of a plane mirror. The instrument is
mounted on heavy supports, under an angle to make it convenient for the
observer. The instrument is finished in first-class manner, and the iron
bed plate heavily copper and nickel plated.

The design of this machine was suggested by Prof. Edwin Frost of the Yerkes
Observatory, where a number of these machines have been in constant use
during the last five years. Careful tests have shown the screw accurate
within .0003 of a mm. throughout the full length. Price           #$175.00#

#Note.#--The micrometer on microscope as shown in cut is not furnished with
instrument.

A tangent screw for revolving the eye piece with the spider thread can be
attached at a cost of $5.00.

[Illustration: A 1201]

[Illustration: A 1202]

#A1202. Comparator for Measuring Spectra Photographs, Scales, Etc.# Range
50 cm. The microscope travels on carefully straightened ways, and is moved
by a screw of 1 mm. pitch. The screw head is faced with a silver band and
is divided in 1000 parts. The handle for turning the screw is placed on the
left side of the instrument so as to have the right hand free for recording
readings.

A set of change gears can easily be engaged to give a fast motion to the
carriage. The stage will hold plates from 3 to 8 cm. in width and of 60 cm.
in length. It can be shifted lengthwise for a distance of 25 cm. and is
provided with adjustment for aligning the plates. The whole stage can be
easily removed from the instrument.

The microscope is fitted with variable magnifying power and is of standard
size. Price                                                       #$450.00#

#Note.#--The design of this comparator was suggested by Prof. Humphries,
Director Laboratory of the U. S. Weather Bureau, for whom the first one was
built.

[Illustration: A 1203]

#A1203. Comparator for Star Photographs#, measures in one direction 80 mm.
and under right angle 60 mm. The lower part is constructed similar to our
Comparator A1201. The top slide carries a divided circle for measuring
position angles. The circle is arranged similar to a position micrometer.
It is fitted with quick gear motion and tangent screw and the two verniers
read to 1-100 degree. The microscope has variable magnifying power and is
provided with reversing eye piece. This machine has been furnished for and
is in use at Yerkes, Lick and Kirkwood Observatories. Price       #$365.00#

[Illustration: A 1204]

#A1204. Comparator.# For Plates 8×10 inches. This machine was constructed
in accordance with suggestions given by Dr. Frank Schlesinger, Director of
Allegheny Observatory. The ways are carefully straightened to within 0.002
millimeter. The carriage is moved by two racks and pinions and has a large
handle on each side. Two concentric circles are fitted to the carriage, the
inner circle carries the plate with the film in a fixed plane, no matter
what the thickness of the glass may be. Both circles are provided with
clamps and tangent screws, so that each one may be clamped and adjusted
independently. The outside circle carries four index points 90 degrees
apart. One of these marks is made adjustable. These four marks serve to
turn the plate exactly 90 degrees so as to measure rectangular
coordinates. The guide carrying the measuring microscope is adjusted
exactly at right angles to the ways of the bed plate. The carriage
supporting the microscope is moved by rack and pinion. The microscope is
arranged to tilt, so as to view either the plate or the scale above. The
eye piece is provided with a reversing prism. Measurements are made on the
scale divided in millimeters. The smaller measurements, to 1-4000 of a mm.,
are made by the micrometer. The micrometer is fitted with sliding eye piece
and counter for full revolutions. The scale is not marked in the usual way
with single lines, but each millimeter is marked with a double line. This
double line allows the use of one single spider thread, which is preferable
to use for bisecting the star, and the double line on the scale allows a
clear setting with the single spider thread. The stage is fitted with an
adaptor for holding plates 4×5 inches. Price                      #$450.00#

This machine has been in use during the last years at the Yerkes
Observatory and has been found very convenient and satisfactory in every
way.

A graduated circle can be provided if desirable. Such division on solid
silver, with verniers reading to 1-100 of a degree will increase the cost
$50.00.

#A1205. Comparator#, for plates 4×5 in. of the same design as A1204.
Price                                                             #$300.00#

[Illustration: A 1206]

#A1206. Comparator.# A larger machine of the same design as A1204 with
scale of 45 cm. length, divided in double lines to 0.25 mm., and with two
carriages, one for spectrum plates of 18 in. length and the other with
divided circles for star photographs 12"×14". This instrument was
constructed for the Solar Observatory of the Carnegie Institution at Mount
Wilson, California.

[Illustration: COELOSTAT.

As built for the United States Naval Observatory after design furnished by
Mr. W. W. Dinwiddie.]

[Illustration: ARMILLARY SPHERE.

Built after design of Prof. J. F. Lanneau, Wake Forest College, N. C.]




_NOVEMBER, 1905_

Wm. Gaertner & Co.

Astronomical, physical and physiological Apparatus


5347-5349 LAKE AVENUE CHICAGO

[Illustration]


Spectrometers and Accessories

#Cat. No. L4020 LABORATORY SPECTROMETER.# This instrument is very rigid and
accurate in construction and every part of its design has been carefully
considered. The circle has a diameter of 15 cm. and the two verniers read
to 20 sec. It is fitted with protecting plate which adds greatly to the
value of the instrument if put in the hands of students. The graduation is
on solid silver. The verniers are fitted with adjustable magnifying
glasses, the telescopes have an aperture of 25 mm., focal length of 200 mm.
A horizontal adjustment for the telescope is provided. No provision is
made for radial adjustment, which correction is made before the instrument
is sent out. The slit is accurately constructed; the jaws are of German
silver and it is provided with comparison prism. The eye end of the
observing telescope is of standard size so as to receive our micrometers
M201 or M202, or the Auto Collimating eye piece (Lamont & Abbe) M540. Gauze
eye piece is fitted to the instrument. The prism table and observing
telescope have independent movements and each is provided with clamp and
tangent screw. The prism table can be clamped to any part of the vernier
plate. The prism holder has convenient leveling arrangement and will hold
prism up to 35 mm. in height. The instrument is arranged to receive Fuess
centering apparatus and crystal holder. A 60 degree heavy flint glass prism
of best optical quality is included.

Price                                                                $75.00

#L4020b CAMERA ATTACHMENT# will fit in place of the observing telescope. It
is fitted with long focus objective and standard plate holder 2½"×2½". The
plate holder is provided with swivel for proper focusing of the spectrum.
The slit is so arranged that four exposures can be made on one plate.

Price                                                                $20.00

#Cat. No. L4020c SCALE TUBE.# The third arm of the instrument can be easily
attached and rotated and clamped in any position. It may also be used for
holding a second Collimator.

Price                                                                $20.00

#Cat. No. L4021 STUDENT'S SPECTROMETER.# This instrument is in every
respect similar to our L4020, but some of the higher finish has been
omitted. All the essentials are carefully constructed and the optical parts
are of the best quality. The circle is protected but only one vernier
reading to 30 sec. is fitted to the instrument. The magnifying glass is
omitted.

Price, including prism                                               $60.00

[Illustration]

[Illustration]


TRANSCRIBERS' NOTES

General: Corrections to punctuation have not been individually noted.

General: Inconsistent spelling of catalog/catalogue preserved as in
original.

Page 7: magnifiing corrected to magnifying and celestrial corrected to
celestial.

Page 17: intensisy corrected to intensity.

Page 18: hundreths corrected to hundredths. LaPlatta as in original.

NB The final two pages of the book, on Astronomical, physical and
physiological Apparatus, are in a slightly different format in the
original. Particularly, prices are not in bold. That has been preserved in
this version.