Produced by Gerard Arthus and the Online Distributed
Proofreading Team at http://www.pgdp.net









  LEARN ONE THING EVERY DAY
  JULY 1 1916   SERIAL NO. 110


  THE MENTOR

  THE WEATHER


  By C. F. TALMAN
  Of The United States Weather Bureau


  DEPARTMENT OF SCIENCE
  $3.00 PER YEAR

  FIFTEEN CENTS A COPY




Old Probabilities


Shall tomorrow's weather be fair or foul? Blow wind--blow moistly from
the South, for I go afishing. "Nay, good friend," exclaims the golfer,
"the day must be dry and the wind in the west." The farmer moistens his
finger and points it toward the sky. "Rain, come, quickly, for my
crops," is his prayer. But the maiden's voice is full of pleading: "Let
the sun shine tomorrow that my heart may be light on my wedding day."

       *       *       *       *       *

And so, through the days and seasons, humanity with all its varied
needs, turns anxiously, entreatingly to Old Probabilities. And how is it
possible for him to satisfy the conflicting demand? He may, on the same
day, please the farmer in the West, the fisherman in the South, the
golfer in the northern hills, and the bride in the eastern town. But how
can he suit them all in one locality on a single day? Old Probabilities
is willing and he loves humanity, but his powers and privileges are
limited. There are those who say that it is due to the kind endeavors of
Old Probabilities to satisfy everybody that our weather has at times
become so strangely mixed.

       *       *       *       *       *

Old Probabilities is a gentle family name and came out of the affection
of the people. The name was a matter of pleasantry. It was given to the
Chief of the United States Weather Bureau when the department was first
established by Congress, and its source lay in the phrase, "It is
probable," with which all the weather predictions began. But Old
Probabilities, genial prophet and lover of his fellow men, is passing
away, for the officer who organized the Weather Bureau became in time
displeased with the name and changed the form of the daily prediction so
as to read, "The indications are." The phrase is formal and severe.
There is naught but cold comfort in it. Our hearts turn back fondly to
Old Probabilities and his friendly assurance: "It is _probable_ that
tomorrow will be fair."




[Illustration: Chickamauga Park, Tenn., in an Ice Storm]

THE WEATHER

By CHARLES FITZHUGH TALMAN

_Librarian of the U. S. Weather Bureau_

THE MENTOR · DEPARTMENT OF SCIENCE · JULY 1, 1916

_MENTOR GRAVURES_

  CENTRAL OFFICE OF THE U. S. WEATHER BUREAU, WASHINGTON, D. C.
  A SIMPLE WEATHER STATION
  A MAJESTIC CUMULUS CLOUD
  THE OBSERVATORY ON MONTE ROSA
  LAUNCHING A METEOROLOGICAL KITE
  THE EFFECTS OF SNOW AND ICE--THE CAMPUS, PRINCETON UNIVERSITY

    [Entered as second-class matter, March 10, 1913, at the postoffice
    at New York, N. Y., under the act of March 3, 1879. Copyright, 1916,
    by The Mentor Association, Inc.]


It is easy to lay too much stress upon the unimportant aspects of
weather. It furnishes a bit of conversation over the teacups; it
accentuates the twinges of rheumatism; it spoils a holiday. All this,
however, is mere byplay.

The real work of the weather--the work that explains the existence of
costly weather bureaus, such as the one upon which our Government spends
more than a million and a half dollars annually--is momentous beyond
calculation. Consider such facts and figures as these:

The head of the British Meteorological Office recently declared that bad
weather costs the farmers of the British Isles about one hundred million
dollars a year. In our own country it has been estimated that a
difference of one inch in the rainfall occurring during July in six
States means a difference of two hundred and fifty million dollars in
the value of the corn (maize) crop. The world over, the damage wrought
by hail-storms is said to average about two hundred million dollars a
year. In the city of Galveston a single hurricane once destroyed twenty
million dollars' worth of property and six thousand human lives. Thus we
might proceed indefinitely.

The fact is that man's welfare is conditioned to an enormous extent and
in an endless variety of ways by the vicissitudes of the atmosphere;
hence the study of weather--meteorology--is one of the most important
of sciences. It is also one of the most strikingly neglected!

At the office of the Weather Bureau in Washington there is a
meteorological library of some thirty-five thousand volumes. But
meteorological libraries are rare; meteorological books are scarce in
other libraries; and meteorologists are so uncommon that whoever
declares himself one is likely to be asked, "What _is_ a meteorologist?"

    [Illustration: STATIONS OF THE UNITED STATES WEATHER BUREAU

    Showing two extreme types: one, an office on the twenty-ninth floor
    of the Whitehall Building, New York City, with instruments installed
    on the roof; the other, an independent observatory building, with
    free exposure on all sides, at St. Joseph, Mo.]

The "meteors" studied by the meteorologist are not shooting stars, but
the phenomena of the atmosphere,--rain and snow, cloud and fog, wind and
sunshine, and whatever else enters into the composition of weather and
climate.


THE ATMOSPHERE

The ocean of air in which human beings live, even as deep-sea fishes
live at the bottom of the liquid ocean, is called the _atmosphere_.
Unlike the liquid ocean, it diminishes rapidly in density from the
bottom upward. At an altitude of three and one-half miles it is only
half as dense as at sea-level. This is higher than the highest permanent
habitations of man. Mountain-climbers and balloonists have attained
greater altitudes; but above a level of about five miles the air is too
greatly rarefied to support life. Balloonists who ascend still higher
must carry a supply of oxygen with them. A little above the ten-mile
level the air is only one-eighth as dense as at sea-level. The
atmosphere extends at least 300 miles above the earth, at which height
its density is computed to be only one two-millionth as great as at
sea-level.

The weather with which human beings are concerned may be said to extend
upward seven or eight miles; _i.e._, to the level of the higher clouds.
The layer of the atmosphere lying between sea-level and the upper cloud
level has certain characteristics that distinguish it from the air above
it, and is known as the _troposphere_.

The heating of the atmosphere by the sun is the beginning of all
weather, and the temperature of the air is the most important weather
element. As soon as we begin to study atmospheric temperature, we
encounter a paradox. The heat of the air is all derived from the sun
(except a minute quantity from the interior of the earth, and an
infinitesimal quantity from other heavenly bodies), and it would
therefore seem at first glance that the upper layers of the atmosphere
should be warmer than the lower. Experience proves the reverse to be the
case. A mountain overgrown with tropical vegetation on its lower slopes
is, if high enough, crowned with eternal snows. A thermometer carried
upward in the air shows under average conditions a fall of temperature
of one degree (Fahrenheit) for every 300 feet of ascent. This fall of
temperature with ascent continues to the upper limit of the troposphere,
where the average temperature is something like 70 degrees below zero.

    [Illustration: THE NEW IDEA IN WEATHER OBSERVATORIES

    The Observatory of the Ebro (Spain), founded by Spanish Jesuits, is
    devoted to studying the interrelations of sun, earth and air. Its
    admirable equipment includes apparatus for the direct and
    spectroscopic study of the sun, for measuring solar radiation,
    atmospheric electricity, earth currents, terrestrial magnetism, and
    earthquakes; besides the ordinary routine of a meteorological
    observatory. The results of all these observations are published
    side by side, to facilitate comparison.]

Above the troposphere is a region called the _stratosphere_, or
_isothermal layer_, in which an ascending thermometer shows irregular
and generally small changes of temperature--not infrequently a rise of
temperature with ascent. The exploration of the stratosphere is one of
the most fascinating fields of meteorological research, but lies
somewhat beyond the scope of an essay on weather. It is carried out
chiefly with the aid of small free balloons, some of which (sounding
balloons) bear self-registering thermometers and other instruments,
while others (pilot balloons) bear no instruments, but show by their
movements the drift of the air currents. The greatest altitude ever
attained by a sounding-balloon was 21.8 miles; by a pilot-balloon, 24.2
miles. The branch of meteorology dealing with the study of the upper air
is called _aërology_.

    [Illustration: A LONELY OUTPOST ON THE VERGE OF THE ANTARCTIC

    The Argentine meteorological station in the South Orkneys. Once a
    year an expedition is sent from Buenos Aires to relieve the staff of
    four observers. This is the southernmost permanently inhabited spot
    on the globe; and it has not even wireless communication with the
    rest of the world.]

Reverting to the temperature of man's environment, the reason why the
atmosphere is warmest at the bottom is this: The sun's rays come to us
from outer space in the form of vibrations in the ether, and warm the
air to only a slight extent in passing through it. They are absorbed by
the ground, and converted into heat waves. The air is then warmed by
contact with the warm ground. Lastly, the warming of the lower air gives
rise to air-currents, which distribute the heat through the atmosphere.


BAROMETRIC PRESSURE

If our weather were uniform, it would furnish little matter for
conversation; in fact, would hardly be weather at all. Changeableness is
the salient feature of weather, and to understand weather changes one
must know something about barometric pressure.

Like all other forms of matter, the invisible air has weight. At
sea-level it exerts a downward pressure averaging 14.7 pounds to the
square inch. Atmospheric pressure is measured by means of an instrument
called the _barometer_, in which the weight of the air is balanced
against a column of mercury. As the height of the mercurial column
varies with the pressure of the air, and is taken as the measure of the
latter, we follow the practice of expressing pressure (a force) in
linear units (inches or millimeters). This practice is retained even in
the use of the aneroid barometer, which contains no mercurial column.
Hence, when we say that the average barometric pressure at sea-level is
29.92 "inches," we are really expressing in a roundabout way the weight
of the air at that level.

    [Illustration: HOW THE CAMERA ANALYZES LIGHTNING

    The same flashes photographed with (_a_) a stationary camera, and
    (_b_) a camera revolving on a vertical axis. One of the flashes is
    seen to have consisted of several successive discharges along an
    identical path

    Courtesy of U. S. Bureau of Standards and Popular Science Monthly.]

Barometric pressure not only varies somewhat regularly with
altitude--diminishing as we ascend--but also less regularly from place
to place in a horizontal direction, and from time to time at a given
place. In studying the weather meteorologists frequently wish to compare
the barometric pressures prevailing at a certain time at a number of
places lying in the same horizontal plane. Given a system of
meteorological stations scattered over a certain territory, the first
step is to secure simultaneous readings of the barometers at these
stations. Then, if the stations are at various altitudes, as they
commonly are, corrections must be applied to the readings to reduce all
to a common plane; the plane adopted for this purpose is sea-level.
Since most stations are _above_ sea-level, and since atmospheric
pressure diminishes with altitude, reduction to sea-level generally
involves applying an _additive_ correction.


THE WEATHER MAP

Now please attend carefully to what follows; because I am going to
attempt to put into a minimum number of words the essential facts
concerning the _weather map_, the best clue to weather mysteries yet
devised by man.

At about 200 stations of the Weather Bureau, distributed over the United
States, the barometer and other meteorological instruments are read
twice a day; viz., at 8 A. M. and 8 P. M., eastern standard time. The
readings are promptly telegraphed in cipher to Washington, where they
are entered on a map.

The barometer readings at the different stations, reduced to sea-level
as just explained, will vary, say, from 29 to 31 inches. Lines, called
_isobars_, are now drawn through places having the same pressure; the
intervals between the lines corresponding to differences in pressure of
one-tenth of an inch. Lines (_isotherms_) are also drawn to connect
places having the same temperature, a little arrow at each station shows
the direction of the wind at that point, and various other symbols are
used to facilitate the interpretation of the map; but the isobars are
more important than anything else.

    [Illustration: CIRRO-STRATUS

    The appearance of this cloud precedes by a day or so the arrival of
    rainy and stormy weather]

    [Illustration: ALTO-CUMULUS]

    [Illustration: FAIR WEATHER CUMULUS

    This cloud marks the summit of an ascending air current, and appears
    toward midday or early afternoon in the warm season. When the air
    rises powerfully to great heights, cumulus is built up in
    mountainous masses and may become cumulo-nimbus, the thundercloud.]

Here is the weather map for the morning of January 9, 1886. The solid
curved lines are isobars, representing barometric pressures ranging all
the way from 28.7 to 30.8 inches. It will be seen at a glance that these
lines tend to assume roughly circular forms, inclosing regions where the
pressure is lower or higher than the average. Moreover, the little
arrows (which "fly with the wind") show that the winds round a center
of low pressure tend to blow in a direction contrary to that followed by
the hands of a clock (in the southern hemisphere the reverse is true),
but instead of blowing in circles are inclined somewhat inward toward
the center. Round a center of high pressure (in the northern hemisphere)
the typical circulation of the winds is exactly opposite ("clockwise,"
and inclined outward), though the accompanying map does not show this
particularly well.

    [Illustration: WEATHER MAP JANUARY 9, 1886]

An area of low pressure, with its system of winds, is called a
_cyclone_, or _low_. An area of high pressure, with its system of winds,
is called an _anticyclone_, or _high_. Note that a cyclone is not
necessarily a storm, though the one shown on this map, with its center
not far from New York City, was a very violent storm, which, when this
map was drawn, was sweeping up the Atlantic coast. (Popular usage
applies the term "cyclone" to the tornado.) The strength of the winds in
a cyclone depends upon the contrast in barometric pressure between its
center and its outer border. A cyclone with crowded isobars always has
strong winds; when the isobars are widely spaced the winds are gentle.

    [Illustration: ASCENT OF A SOUNDING BALLOON

    The first made in the United States; at St. Louis, Mo., in 1904]

These areas of low and high pressure, in addition to their movements
about their centers, move bodily across the country, in a general
west-to-east direction, at an average speed of over 500 miles a day.
This double movement may be compared to that of a carriage-wheel,
rotating and advancing at the same time. Most of our cyclones enter the
country from the Canadian North-west--though many come from other
regions--and nearly all of them pass off to sea in the neighborhood of
the Gulf of St. Lawrence. Their route across the country varies greatly,
depending in part upon the season.

    [Illustration: THE KITE HOUSE AT AN AEROLOGICAL OBSERVATORY

    Some of the kites are much the worse for wear after flying in a
    storm]


THE WEATHER IN CYCLONES AND ANTICYCLONES

Barometric pressure is not an element of weather, in the ordinary sense
of the term, since the fluctuations of pressure that occur in the human
environment are entirely inappreciable to the senses. We have seen,
however, that pressure is intimately related to wind, which is a weather
element of much importance. In noting that systems of high and low
pressure are constantly traveling across the country, and that they are
accompanied by winds having fairly definite characteristics in relation
to each, we have taken an important step toward bringing order out of
the (to the uninitiated) chaotic sequence of weather. Obviously, a
system of telegraphic weather reports makes it possible to keep close
watch of these wind systems, and, from their locations on today's
weather map, to form some idea where they will be tomorrow. Thus the
weather forecaster is enabled to give notice of the imminence of those
violent winds that destroy life and property at sea, and, to a less
extent, on land. There is an element of uncertainty in such
predictions--since storms, unlike railway trains, are not confined to
fixed routes and regular schedules--but the practised forecaster
acquires an instinct that helps him to forestall their vagaries.

    [Illustration: SENDING UP A METEOROLOGICAL BALLOON ON LAKE CONSTANCE

    Between Switzerland and Germany.]

Now what is true of wind is also true to a certain extent of the other
elements of weather,--they bear typical relations to the distribution of
atmospheric pressure. Cyclones are usually preceded by rising
temperature and accompanied by cloudiness and rain or snow;
anticyclones are usually preceded by falling temperature and attended by
fair weather.

Referring again to the map of January 9, 1886, and following the course
of the isotherms, or temperature lines, we see that abnormally cold
weather prevailed over the Middle Western and Southern States. The
isotherm of zero dips far south across northern Texas, Arkansas,
Mississippi, Alabama, and Tennessee; while in the upper Mississippi and
Missouri Valleys the temperatures were from 20 to 40 degrees below zero.
These regions were, in fact, in the grip of a severe "cold wave," which
had entered the country a day or two before, preceding the anticyclone
here seen central north of Dakota. Cold northwesterly winds were
sweeping over the Great Plains, and as far south as the Gulf.

    [Illustration: HOARFROST

    Minute crystals of ice deposited from the air. Under a
    magnifying-glass they show a variety of beautiful forms]

The same map shows typical weather accompanying the cyclone central on
the Atlantic coast. From the seaboard west to the Mississippi Valley
rain or snow had fallen within the previous twenty-four hours (indicated
by shading), and snow (indicated by S) was falling at the moment of
observation at a majority of stations within this area. Elsewhere in the
same region the weather was cloudy.

The foregoing remarks indicate in a general way the significance of the
weather map and the principles upon which scientific weather predictions
are based. The endless procession of highs and lows brings to any place
on the map constant alternations of heat and cold, storm and sunshine.
The forecaster watches the procession, and draws his inferences as to
what will happen in this or that part of the country within the next day
or two (forty-eight hours is about the limit of his outlook).
"Long-range" forecasting is still a thing of the remote future.
Forecasts for a week in advance, are, indeed made by the Weather Bureau
with the aid of reports from a chain of stations extending round the
globe, but these are in very general terms.

    [Illustration: MARVIN RAIN AND SNOW GAGE

    With trumpet-shaped wind-shield at top. In the middle is seen the
    cylindrical collector. This is removed and weighed with its contents
    to ascertain the amount of rain or snow that has fallen]

In January, 1914, the Bureau began publishing a "daily weather map of
the Northern Hemisphere." This publication is, at present, suspended on
account of the war.


SOME WEATHER MISCELLANIES

It would require a book, rather than a brief essay, to describe all the
vicissitudes of weather, and many books that attempt to do this have
been written.[A] We have space here only to mention a few important
features of the weather met with in our own country.

    [A] See "Brief List of Meteorological Textbooks and Reference
        Books," 3d ed., by C. Fitzhugh Talman. For sale by the
        Superintendent of Documents, Washington, D. C. Price 5
        cents.

The southern and southeastern part of a cyclone, some hundreds of miles
from the center, is a favorite breeding-ground for _thunderstorms_ and
_tornadoes_. Thunderstorms of the type known as "heat thunderstorms"
also occur with no special relation to cyclonic centers in regions where
the ground has been intensely heated. In either case the storm is built
up by rapidly ascending air, which cools and condenses its water vapor,
first into enormous clouds (_cumulo-nimbus_, or "_thunderheads_"), and
then into rain, frequently accompanied by hail. It would be necessary to
go to some length to explain the familiar electrical manifestations of
the thunderstorm--some points, indeed, are not perfectly clear to
meteorologists--but it should be stated that these are always the
result, not the cause, of the storm. _Lightning_ is an electrical
discharge between cloud and earth, or cloud and cloud, and _thunder_ is
simply the violent soundwave set up by the sudden expansion of the
heated air along the path of the discharge,--the same acoustic
phenomenon that accompanies an ordinary explosion.

    [Illustration: THE EFFECTS OF AN ICE STORM AT CANTON, N. Y. March
    25-27, 1913]

    [Illustration: SUMMIT HOTEL AT SUMMIT, CAL.

    On March 18, 1911. A three-story building whose first story is
    buried under twenty-six feet of snow]

A _tornado_ (popularly miscalled a "cyclone") is an extremely violent
vortex in the air, usually less than 1,000 feet in diameter. Besides its
very rapid rotary motion, it has a progressive motion at a speed
averaging forty or fifty miles an hour. Its position at any moment is
marked by a black funnel-shaped cloud, which grows downward from the sky
and does not at all times reach the earth. A waterspout at sea is an
identical phenomenon, though usually less violent. Along its narrow path
the tornado demolishes everything,--wooden houses are blown to
splinters, trees uprooted or stripped of their branches, structures of
heavy masonry laid in ruins. Something like a hundred lives are lost
each year in these storms, on an average, and one of them (St. Louis,
May 27, 1896) destroyed thirteen million dollars' worth of property.

    [Illustration: Courtesy of the Scientific American

    A WATERSPOUT NEAR BEAUFORT, N. C., IN AUGUST, 1911]

    [Illustration: TURPAIN'S THUNDERSTORM RECORDER

    Or ceraunograph. This is one of several instruments designed to
    register the natural electric waves, or "strays," which sometimes
    interfere seriously with the transmission of wireless telegrams.
    Strays are often generated by lightning discharges, near or distant,
    and this instrument therefore serves to give notice of an
    approaching thunderstorm]

A _blizzard_ is a high, cold wind, accompanied by blinding snow, which
in winter sometimes blows out of the front of an advancing anticyclone,
especially in our North-Central States. A similar wind, with or without
snow, is called in Texas a _norther_.

A _chinook_ is a warm, dry wind that descends the eastern slope of the
Rocky Mountains in Montana, Wyoming and Colorado, and flows
north-eastward over the plains. Its effects are most pronounced in
winter, when it brings about a very sudden rise in the temperature--in
extreme cases as much as forty degrees in fifteen minutes! It causes
snow to vanish as if by magic, and is appropriately nicknamed the
"snow-eater."

"_Cloudburst_" is merely a picturesque name for a very heavy shower;
usually a thunder-shower.

    [Illustration: IN THE WAKE OF A TORNADO

    The tornado destroyed a house and barn, but left a path in the
    center with practically no harm done]

_West India hurricanes_ occasionally visit the United States, especially
in the late summer and early autumn. These storms begin as violent
cyclones of small extent (300 to 600 miles in diameter), usually
somewhere east of the West Indies, sweep in a long curve across the
Caribbean Sea, and then turn north, either passing up along the
Atlantic Coast or crossing the Gulf of Mexico into the southern United
States. Soon after entering the temperate zone they increase in size and
diminish in violence, but are still vigorous enough on reaching the Gulf
or South Atlantic Coast to cause great devastation. Low-lying shores are
often inundated by the immense waves they generate.

_Cold waves_ are the rapid and severe falls in temperature that
sometimes occur in winter, especially at the front of an anticyclone.
Warnings of these occurrences, issued by the Weather Bureau twenty-four
to thirty-six hours in advance, often result in the saving of millions
of dollars' worth of merchandise susceptible to damage by freezing.

_Frosts_ in the spring and autumn are also predicted with great success,
to the immense advantage of farmers, market-gardeners, and
horticulturists. The practice of smudging or heating orchards, now so
widespread, is usually carried on under the advice of the Weather
Bureau, which gives prompt notice to the orchardist when such
precautions are in order. The bureau publishes charts showing the
average and extreme dates of the last frost in spring and the first
frost in autumn for all parts of the country.

    [Illustration: LOOKING DOWN ON A SEA OF FOG FROM MT. TAMALPAIS,
    CALIFORNIA]

A _fog_ is a cloud resting on the surface of the earth. In the United
States fog is commonest along the northern and middle parts of the
Atlantic and Pacific Coasts. In the interior of the country, especially
the western part, it is of rare occurrence, the average number of days a
year with fog being less than ten.

Lastly--weather fallacies are rife. _Indian summer_ is merely a type of
mild, hazy, heavenly weather that prevails intermittently during our
long American autumns. The _equinoctial storm_ is a myth; the climate
has not "changed" anywhere within the span of a human lifetime (one year
differs from another, but there is no progressive or permanent change);
and the _moon_ has nothing whatever to do with THE WEATHER.




SUPPLEMENTARY READING


  CLIMATE AND WEATHER                             _By H. N. Dickson_

  AMERICAN WEATHER                                 _By A. W. Greely_

  WEATHER SCIENCE                             _By R. G. K. Lempfert_

  SOME FACTS ABOUT THE WEATHER                      _By W. Marriott_
    Second edition.

  METEOROLOGY                                      _By W. I. Milham_
   The latest general textbook on the subject in English.

  FORECASTING WEATHER                                _By W. N. Shaw_

  ELEMENTARY METEOROLOGY                               _By F. Waldo_

Consult also the numerous publications of the United States Weather
Bureau, which will be found in most public libraries.


*** Information concerning the above books and articles may be had on
application to the Editor of The Mentor.




THE OPEN LETTER


"What is lightning and what causes it?" The question came to us a few
days after we had made announcement of a "Weather" number of The Mentor.
It was a natural question, for lightning is the most sensational of all
weather phenomena. It has always had a fearful sort of fascination for
humanity. To the ancients it came as a bolt of wrath from the hand of
Jove. To the fire-worshipers it was a warning message. To parched
travelers it was a bright promise, for it heralded the coming of rain.
To the superstitious it was a signal flash from the spirit world. And to
those of nervous temperament it was a highly disturbing phenomenon
producing emotions varying from uneasiness and alarm to hysteria. The
question then, "What is lightning and what causes it?" has an interest
for all. I referred it to Mr. Talman, the author of the Mentor article
on "The Weather." His reply follows.

       *       *       *       *       *

"Not so many generations ago 'natural philosophers' thought that
inflammable gases, exhaled from the earth, took fire spontaneously in
the air, and that this was lightning. The idea also prevailed--and it is
not yet quite extinct--that a stroke of lightning involved the hurling
down from the sky of a mass of rock, called a 'thunderbolt.' In the
eighteenth century people became quite familiar with the process of
generating, by friction, a mysterious something called 'electricity,'
which, when it passed from one body to another through a small layer of
intervening air, produced sparks. Several philosophers noticed the
resemblance between these sparks and lightning. It remained, however,
for Benjamin Franklin to prove that lightning was really an electrical
discharge on a large scale. The experiments by which he proposed to
demonstrate this were successfully performed, first by others, in
France, and then, by Franklin himself, at Philadelphia. With the aid of
his famous kite he drew down from a thundercloud a little of the
'electrical fluid' (as it was then called), and produced tiny sparks
from an iron key at the lower end of the wet kite-string.

"We do not even yet know what electricity is, but we know a great deal
about the way it behaves and the effects it produces. There are two
kinds of electricity, which we call _positive_ and _negative_. A body is
said to be _charged_ when it has an excess of either kind, and the two
kinds have a tendency to unite and neutralize each other's effects.
Thunderclouds become heavily charged with electricity. We are not quite
sure how this happens, but it is now commonly believed that the strong
uprising currents of air that occur in the storm, in the process of
breaking up the water-drops in the cloud also separate positive from
negative electricity; leaving the former in excess in the part of the
cloud next to the earth, and carrying the latter far aloft.

"By a process called 'induction' the positive charge in the cloud draws
an excess of negative electricity to the surface of the ground
underneath. The stronger the contrast between these opposite charges,
the harder they try to break through the interposing barrier of the air
(which is a poor conductor of electricity) and to neutralize each other.
At length they succeed in doing so. A powerful stream of electricity
flows for an instant between cloud and earth. Its passage heats the air
and makes it luminous--just as the passage of an electric current heats
the filament of an electric lamp and makes it luminous. This is
lightning.

"These discharges occur not only between the clouds and the earth, but
also, and probably more often, between clouds charged with opposite
kinds of electricity.

"The sudden expansion of the heated air along the path of the discharge
affects our ears just as does the sudden expansion of the air at the
mouth of a gun when it is fired. In each case a wave is sent through the
air in all directions from the place of disturbance, and our ear-drums
are set in vibration. That is thunder."

       *       *       *       *       *

Take courage then, you timid ones, who wince in the lightning's flash
and tremble under the thunder's roll. Thunder is simply a vibration of
your ear drums--and, when you hear the thunder, be assured, all danger
is over.

                                             [Signature: W. D. Moffat]

                                                                EDITOR




THE MENTOR ASSOCIATION

    ESTABLISHED FOR THE DEVELOPMENT OF A POPULAR INTEREST IN
    ART, LITERATURE, SCIENCE, HISTORY, NATURE, AND TRAVEL


THE PLAN OF THE ASSOCIATION

The purpose of The Mentor Association is to give its members, in an
interesting and attractive way the information in various fields of
knowledge which everybody wants and ought to have. The information is
imparted by interesting reading matter, prepared under the direction of
leading authorities, and by beautiful pictures, reproduced by the most
highly perfected modern processes.

The object of The Mentor Association is to enable people to acquire
useful knowledge without effort, so that they may come easily and
agreeably to know the world's great men and women, the great
achievements and the permanently interesting things in art, literature,
science, history, nature, and travel.

The purpose of the Association is carried out by means of simple
readable text and beautiful illustrations in The Mentor.

The annual subscription is Three Dollars, covering The Mentor Course,
which comprises twenty-four numbers of The Mentor in one year.


    THE MENTOR IS PUBLISHED TWICE A MONTH

    BY THE MENTOR ASSOCIATION, INC., AT 52 EAST NINETEENTH STREET, NEW
    YORK, N. Y. SUBSCRIPTION, THREE DOLLARS A YEAR. FOREIGN POSTAGE 75
    CENTS EXTRA. CANADIAN POSTAGE 50 CENTS EXTRA. SINGLE COPIES FIFTEEN
    CENTS. PRESIDENT, THOMAS H. BECK; VICE-PRESIDENT, WALTER P. TEN
    EYCK; SECRETARY, W. D. MOFFAT; TREASURER, ROBERT M. DONALDSON; ASST.
    TREASURER AND ASST. SECRETARY, J. S. CAMPBELL


    THE MENTOR ASSOCIATION, INC.
    52 EAST 19th STREET, NEW YORK N. Y.




THE MENTOR

The Mentor Index


An index to The Mentor has been prepared, and is now ready. Every number
of The Mentor, from Serial No. 1 through 106, has been indexed. It is a
complete, concise, and accurate grouping of all the subjects treated in
The Mentor, under three headings--the gravure pictures, the monographs,
and The Mentor articles. Every subject is carefully indexed so that the
information desired may be quickly and easily found.

Every member of The Mentor Association should own this index, and every
member will want to own it, particularly if his or her file of back
numbers is complete.

The index is the same size as The Mentor and similar in style, so that
it may be bound in with the numbers of The Mentor themselves. The price
is twenty-five cents a copy. It would be advisable to place your order
at once, as the first edition is limited.


_Send all orders to_

  THE MENTOR ASSOCIATION
  52 EAST NINETEENTH STREET
  NEW YORK, N. Y.


MAKE THE SPARE MOMENT COUNT




CONTRIBUTORS TO THE MENTOR


These are the men and women who make The Mentor--all of them eminent
authorities in their special fields of knowledge.

    JOHN C. VAN DYKE, Professor of the History of Art, Rutgers College,
      and Author of many books.

    HAMILTON W. MABIE, Editor of The Outlook, and Author and Literary
      Critic.

    DWIGHT L. ELMENDORF, Traveler and Lecturer.

    ALBERT BUSHNELL HART, Professor of Government, Harvard University.

    DR. WILLIAM T. HORNADAY, Director of the New York Zoological Park,
      and Author of many nature books.

    ROBERT E. PEARY, Discoverer of the North Pole.

    PROF. CHARLES E. FAY, Tufts College, and First President of the
      American Alpine Club.

    WILLIAM WINTER, celebrated Critic and Author.

    JAMES HUNEKER, Author and Critic.

    GUSTAV KOBBÉ, Art Critic of the New York Herald, and Author of many
      books.

    LORADO TAFT, well-known American Sculptor and Author.

    W. J. HENDERSON, Music Critic of the New York Sun, and Author of
      many books.

    STEPHEN BONSAL, Author and War Correspondent.

    E. H. FORBUSH, State Ornithologist of Massachusetts, and Author of
      many books.

    BURGES JOHNSON, Professor, Vassar College, Author and Humorist.

    ARTHUR HOEBER, Artist, Critic and Author.

    DANIEL C. BEARD, Author, Artist, and celebrated Naturalist.

    SAMUEL ISHAM, distinguished Art Critic and Author.

    H. ADDINGTON BRUCE, Author of many books.

    PROF. C. R. RICHARDS, Director of Cooper Union, New York City.

    ROBERT M. McELROY, Professor of American History, Princeton
      University.

    CLARENCE WARD, Professor of Architecture, Rutgers College.

    IDA M. TARBELL, well-known Magazine Writer and Author of many books.

    HENRY T. FINCK, Music Editor of the New York Evening Post, and
      Author of various books.

    J. T. WILLING, Art Editor and Author.

    GEORGE W. BOTSFORD, Professor of Ancient History, Columbia
      University.

    H. E. KREHBIEL, Music Critic of the New York Tribune, and Author of
      various books.

    F. J. MATHER, Jr., Professor of Art and Archeology, Princeton
      University.

    FREDERICK PALMER, Celebrated War Correspondent, and Author of
      various books.

    HENRY WOODHOUSE, Editor of "Flying," and an authority on
      aeronautics.

    WILLIAM A. COFFIN, N. A., well-known Artist and Author.

    KENYON COX, N. A., distinguished Artist, Author and Instructor in
      art.

    ESTHER SINGLETON, Author of many books.

    WALTER PRICHARD EATON, well-known Magazine Writer and Author of
      various books.

    JOHN K. MUMFORD, Author and Expert on rugs.

    BELMORE H. BROWNE, Artist, Author and Explorer.

    FRANK WEITENKAMPF, of the New York Public Library, Expert In Prints.

    W. J. HOLLAND, Director of the Carnegie Museum, Pittsburgh, Pa., and
      distinguished Naturalist.

    DEAN C. WORCESTER, noted Traveler and Lecturer and Author.

    AYMAR EMBURY, well-known Architect and Writer on architectural
      subjects.

    C. F. TALMAN, of the United States Weather Bureau, Washington.




Complete Your MENTOR LIBRARY

SUBSCRIPTIONS ALWAYS BEGIN WITH THE CURRENT ISSUE


The following numbers of The Mentor Course, already issued, will be sent
postpaid at the rate of fifteen cents each.

  Serial No.

    1. Beautiful Children in Art
    2. Makers of American Poetry
    3. Washington, the Capital
    4. Beautiful Women in Art
    5. Romantic Ireland
    6. Masters of Music
    7. Natural Wonders of America
    8. Pictures We Love to Live With
    9. The Conquest of the Peaks
   10. Scotland, the Land of Song and Scenery
   11. Cherubs in Art
   12. Statues With a Story
   13. Story of America in Pictures: The Discoverers
   14. London
   15. The Story of Panama
   16. American Birds of Beauty
   17. Dutch Masterpieces
   18. Paris, the Incomparable
   19. Flowers of Decoration
   20. Makers of American Humor
   21. American Sea Painters
   22. Story of America in Pictures: The Explorers
   23. Sporting Vacations
   24. Switzerland: The Land of Scenic Splendors
   25. American Novelists
   26. American Landscape Painters
   27. Venice, the Island City
   28. The Wife in Art
   29. Great American Inventors
   30. Furniture and Its Makers
   31. Spain and Gibraltar
   32. Historic Spots of America
   33. Beautiful Buildings of the World
   34. Game Birds of America
   35. Story of America in Pictures: The Contest for North America
   36. Famous American Sculptors
   37. The Conquest of the Poles
   38. Napoleon
   39. The Mediterranean
   40. Angels in Art
   41. Famous Composers
   42. Egypt, the Land of Mystery
   43. Story of America in Pictures: The Revolution
   44. Famous English Poets
   45. Makers of American Art
   46. The Ruins of Rome
   47. Makers of Modern Opera
   48. Durer and Holbein
   49. Vienna, the Queen City
   50. Ancient Athens
   51. The Barbizon Painters
   52. Abraham Lincoln
   53. George Washington
   54. Mexico
   55. Famous American Women Painters
   56. The Conquest of the Air
   57. Court Painters of France
   58. Holland
   59. Our Feathered Friends
   60. Glacier National Park
   61. Michelangelo
   62. American Colonial Furniture
   63. American Wild Flowers
   64. Gothic Architecture
   65. The Story of the Rhine
   66. Shakespeare
   67. American Mural Painters
   68. Celebrated Animal Characters
   69. Japan
   70. The Story of the French Revolution
   71. Rugs and Rug Making
   72. Alaska
   73. Charles Dickens
   74. Grecian Masterpieces
   75. Fathers of the Constitution
   76. Masters of the Piano
   77. American Historic Homes
   78. Beauty Spots of India
   79. Etchers and Etching
   80. Oliver Cromwell
   81. China
   82. Favorite Trees
   83. Yellowstone National Park
   84. Famous Women Writers of England
   85. Painters of Western Life
   86. China and Pottery of Our Forefathers
   87. The Story of The American Railroad
   88. Butterflies
   89. The Philippines
   90. Great Galleries of the World: The Louvre
   91. William M. Thackeray
   92. Grand Canyon of Arizona
   93. Architecture in American Country Homes
   94. The Story of The Danube
   95. Animals in Art
   96. The Holy Land
   97. John Milton
   98. Joan Of Arc
   99. Furniture of the Revolutionary Period
  100. The Ring of the Nibelung
  101. The Golden Age of Greece
  102. Chinese Rugs
  103. The War of 1812
  104. Great Galleries of the World: The National Gallery, London
  105. Masters of the Violin
  106. American Pioneer Prose Writers
  107. Old Silver
  108. Shakespeare's Country
  109. Historic Gardens of New England


NUMBERS TO FOLLOW

July 15. AMERICAN POETS OF THE SOIL. _By Burges Johnson, Associate
Professor of Literature, Vassar College._

August 1. ARGENTINA. _By E. M. Newman, Lecturer and Traveler._


       *       *       *       *       *




[Illustration: CENTRAL OFFICE OF THE UNITED STATES WEATHER BUREAU,
WASHINGTON, D. C.]

WEATHER SERVICES AT HOME AND ABROAD

Monograph Number One in The Mentor Reading Course


Posted up in public offices, in hotel corridors, and other conspicuous
places in our cities, the official weather map is a familiar sight. Even
more familiar is the official weather forecast, displayed, as a rule, on
the first page of the daily newspaper, and sent broadcast over the
country on the little brown cards which one may see in the village
postoffice as well as in the city drug-store. When a great storm sweeps
over land or sea, detailed official reports concerning its progress and
characteristics are published in the daily press. When a lawsuit
involves a dispute as to the temperature or the state of the sky on a
certain day, the official weather records are consulted.

How much do you know about the branch of the national government that is
charged with the duty of keeping watch of the weather--recording its
vagaries as they occur, and also predicting them, as far as is humanly
possible?

Besides its office in Washington, where more than two hundred persons
are constantly employed, the Weather Bureau has about two hundred
stations, manned by professional meteorologists and observers. One of
these will be found in almost every large city, while some are in towns
of very modest importance. A regular Weather Bureau station is well
worth a visit. The instrumental equipment of these stations is almost
superhuman in the accuracy with which it sets down on paper the
chronicle of weather happenings from day to day and from moment to
moment. Little less marvelous is the system by means of which weather
information--past, present and future--is disseminated from these
official foci. The postoffice, the telephone, the telegraph (wire and
wireless) are all pressed into service to the fullest extent--especially
in giving timely notice of approaching storms and other destructive
forms of weather. These agencies are supplemented by visible and audible
signals, in the shape of flags, lanterns, railway whistles and so forth.

Contrary to popular belief, the Weather Bureau does not exist primarily
for the purpose of telling the public (with a considerable margin of
uncertainty) whether it will be advisable, on the morrow, to carry an
umbrella or wear an overcoat. The important work of the Bureau is
twofold. It consists, first, in the prediction of those atmospheric
visitations, such as storms, floods, and cold waves, which endanger life
and property on a large scale; and, second, in the maintenance of the
records that form the basis of climatic statistics. In both these
directions the Bureau splendidly justifies its existence.

Our national weather service was founded in 1870, and for twenty years
was maintained by the Signal Corps of the Army. In 1890 it was
established on the present basis, as the Weather Bureau of the
Department of Agriculture.

Most civilized countries possess official services for the observation
and prediction of weather, though no other is organized on quite so
grandiose a scale as ours. The British Meteorological Office, the
Prussian Meteorological Institute, the Central Meteorological Bureau of
France, and the Central Physical Observatory of Petrograd are among the
leading institutions of this character in the Old World. Admirable
weather services also exist in India, Japan, Australia, Canada,
Argentina and elsewhere.




[Illustration: A SIMPLE WEATHER STATION]

METEOROLOGICAL INSTRUMENTS

Monograph Number Two in The Mentor Reading Course


The history of meteorological instruments dates back at least as far as
the fourth century before the Christian era, when the depth of rainfall
was measured in India by some form of gauge. We again hear of
rain-gauges being used in Palestine in the first century of the present
era. Thermometers with fixed scales were used in Italy in the
seventeenth century, and the great Galileo, born in Pisa in 1564, took
part in perfecting these instruments. Wind-vanes were known to the
ancients. The earliest one of which we have any record surmounted the
famous Tower of the Winds at Athens. In the Middle Ages the weathercock
became the usual adornment of church steeples. The barometer was
invented by Torricelli in 1643.

Most meteorological instruments, however, are of quite recent origin,
and this is true especially of these types of apparatus that make
automatic records, thus replacing, to a large extent, the human
observer.

Our picture on the other side of this sheet shows the instruments used
by the "co-operative" observers of the Weather Bureau. These observers,
of whom there are about 4,500, well distributed over the country, serve
the government without pay, and their painstaking observations have
alone made possible a detailed survey of our climate. In the picture we
see, on the right, an ordinary rain-gauge, and, on the left, a
thermometer-screen containing two thermometers; viz., a maximum
thermometer, for recording the highest temperature of the day, and a
minimum thermometer, for recording the lowest. The screen, which is of
wood, painted white, serves to shield the instruments from the rays of
the sun, while permitting free ventilation. Under these conditions the
thermometers show the temperature of the _air_; whereas when exposed to
direct sunlight a thermometer shows the temperature acquired by the
instrument itself, and this may differ materially from the air
temperature.

In contrast to this simple equipment, we find at a regular
meteorological station, or observatory, an impressive collection of
apparatus for observing and recording nearly all the elements of
weather. The pressure of the air is measured by the mercurial barometer,
and registered continuously by the barograph; the temperature of the air
is automatically recorded by the thermograph. Other self-registering
instruments maintain continuous records of the force and direction of
the wind, the amount and duration of rainfall, the duration of sunshine,
the humidity of the air, etc. There are also instruments for measuring
evaporation, the height and movement of clouds, the intensity of solar
radiation, the elements of atmospheric electricity, and various other
phenomena of the atmosphere.




[Illustration: A MAJESTIC CUMULUS CLOUD]

CLOUDS AND RAINFALL

Monograph Number Three in The Mentor Reading Course


The International Cloud Classification, now generally used by
meteorologists, is an amplification of one introduced by an
ingenious English Quaker, Luke Howard, in the year 1803. Howard
distinguished seven types of cloud, to which he gave the Latin names
_cirrus_, _cumulus_, _stratus_, _cirro-cumulus_, _cirro-stratus_,
_cumulo-stratus_, and _nimbus_. In passing, it may be of interest to
note that, a few years after Howard's classification was published,
an attempt was made by one Thomas Forster to introduce "popular"
equivalents of these terms. Forster proposed to call cirrus "curlcloud,"
cumulus "stackencloud," stratus "fallcloud," etc. In other words,
he assumed that because Howard's names were Latin in form they
were unsuitable for use by the layman, and therefore needed to be
supplemented by English names--although the proposed substitutes were,
on the whole, somewhat longer and more difficult to pronounce than the
originals! A parallel undertaking would be an attempt to discourage
the public from calling the wind-flower "anemone," or virgin's bower
"clematis." Forster's superfluous names have never taken root in our
language.

The highest clouds--cirrus and cirro-stratus--are feathery in
appearance, and consist of minute crystals of ice. Their altitude above
sea-level averages about five miles, but is frequently much greater
than this. All other clouds are composed of little drops of water--not
hollow vesicles of water, as was once supposed. Neither crystals nor
drops actually "float" in the air. They are constantly falling with
respect to the air around them, though, as the air itself often has an
upward movement, the cloud particles are not always falling with
reference to the earth. In any case, their rate of fall depends upon
their size, and in the case of the smaller particles is very slow. Under
some conditions the particles evaporate before reaching the earth, while
under others they maintain a solid or liquid form and constitute rain or
snow. A fog is a cloud lying at the earth's surface.

Rainfall is one of the most important elements of climate, chiefly
because of its effects upon vegetation. It is measured in terms of the
depth of water that would lie on the ground if none of it ran off,
soaked in, or evaporated; and this is, in practice, determined by
collecting the rain, as it falls, in a suitable receiver, or rain-gauge.
Usually the gauge is so shaped as to magnify the actual depth of
rainfall, in order to facilitate measurement. Snow is measured in two
ways; first, as snow, and, second, in terms of its "water equivalent."
The latter measurement is commonly effected by melting the snow and
pouring it into the rain-gauge, where it is measured as rain. By this
expedient we are enabled to combine measurements of rain and snow, in
order to get the total "precipitation" of a place during a given period.

Nature is notoriously partial in her distribution of this valuable
element over the earth. A region having an average annual rainfall of
less than ten inches is normally a desert, though irrigation or
"dry-farming" methods may enable its inhabitants to practice
agriculture.

The heaviest average annual rainfall in the United States (not including
Alaska) is about 136 inches, in Tillamook County, Oregon. The rainiest
meteorological station in the world is Cherrapunji, India, with an
average of about 426 inches per annum.[B]

    [B] This is the latest official record. There are several
        rain-gauges at Cherrapunji, and the average amount of
        rain collected by any one of them varies considerably
        with the length of the record. Hence the widely divergent
        values of the rainfall at this famous station published
        in encyclopædias and other reference books.




[Illustration: THE OBSERVATORY ON MONTE ROSA]

THE OUTPOSTS OF METEOROLOGY

Monograph Number Four in The Mentor Reading Course


The expression used in our title seems a fitting one to apply to a
number of meteorological observatories and stations maintained for the
benefit of science in regions remote from the comforts and conveniences
of civilization. Some are on the summits of lofty mountains, the ascent
of which is laborious and even perilous. Others are situated in the
bleak wildernesses of the circumpolar zones. Public attention has all
too rarely been called to the heroism and self-sacrifice of the men who
constitute the staffs of these lonely outposts.

The institution shown in our gravure--officially known, in honor of the
Dowager Queen of Italy, as the Regina Margherita Observatory--crowns the
summit of Monte Rosa, on the northern Italian frontier, and is 14,960
feet above sea-level. It is devoted not only to meteorological
investigations, but to studies of the physiological effects of great
altitudes and various other researches, and is open to the _savants_ of
all nationalities who are courageous enough to scale the second highest
summit of the Alps. It is habitable for only about two months; viz.,
from the middle of July to the middle of September. Each year a
temporary telephone line is constructed connecting the observatory with
the plains of Italy. This is the highest telephone line in the world,
and its installation is an arduous undertaking. A permanent line is
impossible, on account of the shifting of the glaciers and snowfields on
which the poles must be erected.

There is also a meteorological observatory on Mont Blanc, but it is not
at the summit and is not quite so high as that on Monte Rosa. The solar
observatory which once stood at the very top of Mont Blanc no longer
exists. The United States Signal Service (now the Weather Bureau)
formerly maintained observatories on Pike's Peak (14,134 feet) and Mount
Washington (6,280 feet). The loftiest of meteorological stations was,
however, that formerly operated by Harvard College Observatory on the
summit of El Misti, Peru (19,200 feet).

For a number of years the United States Weather Bureau maintained a
large and important observatory at Mount Weather, at the crest of the
Blue Ridge, near Bluemont, Virginia. In the Old World one of the most
famous of mountain meteorological observatories was that which stood on
Ben Nevis (4,406), the highest summit in the British Isles. This was
closed in 1904.

If the conditions of life at these high-level stations are such as to
repel any but the ardent lover of science, the same is true in even
greater measure of those endured by the little band of meteorologists
who man the observatory maintained by the government of Argentina at
Laurie Island, in the South Orkneys, on the verge of the Antarctic.
Every year a party of four is sent out from Buenos Aires to spend a year
of exile in this inhospitable spot, which is generally ice-bound, and
has not even wireless communication with the rest of the world. This
station has been in operation since 1904. The staff, which is changed
each year, has embraced men of several nationalities--Scotch, American
and others.

Far within the Arctic Circle two meteorological observatories are
maintained in Spitsbergen; but these are, at least, connected with the
world by radiotelegraphy.

If the hopes of explorer Peary are accomplished, an observatory will,
one of these days, be established at the South Pole.




[Illustration: LAUNCHING A METEOROLOGICAL KITE]

THE AIR ABOVE US

Monograph Number Five in The Mentor Reading Course


Meteorologists are not content to limit their investigations to the
stratum of air lying close to the earth's surface. Even before the
demands of the aeronaut for information concerning the structure and
phenomena of the atmosphere far overhead became pressing, many efforts
had been made to secure such information, in view of its important
bearing upon many scientific problems. As long ago as the year 1784 a
balloonist, equipped with various meteorological instruments, made an
ascent from London and brought back an interesting series of
observations, which were communicated to the Royal Society. For more
than a century the manned balloon was the principal means of sounding
the upper atmosphere.

Nowadays, as a rule, the meteorologist, instead of going aloft in
person, sends up a kite or a balloon to which are attached automatically
registering instruments. When the aerial vehicle returns to earth its
record shows in detail the conditions encountered during the journey.

Everybody remembers how Franklin brought lightning from the clouds; but
it is a far cry from the simple apparatus that served Franklin's purpose
to the "box kite" of modern meteorology. Science has perfected the kite
almost beyond recognition. It has been shorn of that crucial feature of
the schoolboy article, the tail. Even the kite "string" has become
several miles of steel piano wire, wound around the drum of a
power-driven winch, with elaborate apparatus for recording the force of
the pull, and the angles of azimuth and altitude.

Captive balloons are sometimes used for similar investigations. When,
however, it is desired to attain great altitudes the meteorologist has
recourse to the so-called "sounding-balloon," which is not tethered to
the earth. This is usually made of india-rubber, and when launched is
inflated to less than its full capacity. As it rises to regions of
diminished air pressure it gradually expands, and finally bursts at an
elevation approximately determined in advance. A linen cap, serving as a
parachute, or sometimes an auxiliary balloon which does not burst,
serves to waft the apparatus, with its delicate self-registering
instruments, gently to the ground. This commonly happens many
miles--sometimes two hundred or more--from the place of ascent. Attached
to the apparatus is a ticket offering the finder a reward for its
return, and giving instructions as to packing and shipping. Sooner or
later it usually comes back; though often months after it falls. Indeed,
the large percentage of records recovered, even in sparsely settled
countries, is not the least remarkable feature of this novel method of
research. The instruments attached to sounding-balloons register the
temperature of the air, the barometric pressure, and sometimes the
humidity.

By means of the sounding-balloon the air is explored to heights of
twenty miles and more! The records obtained by means of these balloons
have, within the past fifteen years, completely revolutionized our ideas
concerning the upper atmosphere.

Still another device employed by meteorologists is the pilot-balloon.
This is also a free balloon, but carries no meteorological instruments.
Its motion in the air is followed by means of a theodolite, and it
serves to show the speed and direction of the wind at different levels.
During the winter of 1912-13 a pilot-balloon sent up from Godhavn,
Greenland, by a Danish exploring expedition reached the unprecedented
altitude of more than 24 miles.




[Illustration: THE EFFECTS OF SNOW AND ICE--THE CAMPUS, PRINCETON
UNIVERSITY]

OUR WINTERS

Monograph Number Six in The Mentor Reading Course


In the year 1781 Thomas Jefferson wrote in his "Notes on Virginia":
"A change of climate is taking place very sensibly. *** Snows are less
frequent and less deep. They do not often lie below the mountains
more than one, two or three days, and very rarely a week. The snows
are remembered to have been formerly frequent, deep, and of long
continuance. The elderly inform me that the earth used to be covered
with snow about three months in every year."

Probably long before the white man came to America the patriarchs of the
Indian tribes regaled the young men and maidens gathered about the
campfire with reminiscences of the deep snows that prevailed in a
previous generation.

In short the "old-fashioned winter" is a _perennial myth_, perpetuated
by a familiar process of self-delusion! The occasional periods of
abundant snow make a more lasting impression upon our minds than the
long intervals in which this element was scarce or lacking. The
resulting misconception is promptly dissipated when we consult the
weather records, which, in some parts of the country, extend back more
than a century, and prove that there has been no actual change in the
climate within the period they embrace.

Of course the erroneous idea is, in some cases, due to the fact that
one's childhood was spent in a part of the country in which the snowfall
is normally heavier than in that where one has recently lived. The
average yearly snowfall over the New England States, New York, and the
borders of the Great Lakes is from 50 to 100 inches, and upward. Over
the North Central States it is much less. In the Southern tier of States
and along almost the whole of our Pacific coast snow is a rarity. The
heaviest snowfall in this country probably occurs in the high Sierra
Nevada of California, near the border of Nevada. In some places in these
mountains more than 40 feet of snow falls in an average winter, while
more than 65 feet has been recorded in extreme cases. Here it is a
common occurrence for one-story houses to be buried, to the eaves, or
above. The Southern Pacific Railway, which intersects this region, has
built 32 miles of snowsheds, at a cost of $42,000 a mile over single
track and $65,000 a mile over double track. In an average year $150,000
is spent on these sheds in upkeep and renewals. Flat-roofed houses are
unknown in this vicinity; all roofs are gabled at a sharp angle to shed
the snow.

A picturesque feature of our American winters is the "ice storm," so
enthusiastically described by Mark Twain:

"... When a leafless tree is clothed with ice from the bottom to the
top--ice that is as bright and clear as crystal; when every bough and
twig is strung with ice-beads, frozen dew-drops, and the whole tree
sparkles cold and white, like the Shah of Persia's diamond plume."

Such is the artist's view of the phenomenon; but, alas! these same ice
storms cause endless inconvenience and heavy expense every winter to the
electrical industries, by breaking wires.


    PREPARED BY THE EDITORIAL STAFF OF THE MENTOR ASSOCIATION
    ILLUSTRATION FOR THE MENTOR, VOL. 4, No. 10, SERIAL No. 110
    COPYRIGHT, 1916, BY THE MENTOR ASSOCIATION, INC.






End of Project Gutenberg's The Mentor: The Weather, by Charles Fitzhugh Talman