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The small dials show what time it is in those states and countries of America and Europe that use Standard Greenwich time, when it is 12 o'clock in New York. France and Portugal have just adopted Greenwich time.

Copyright 1910

by Munn

& Co., Inc.

The Simplex Perpetual Calendar.

Giving the days of the week of any month of any year of the Christian Era, and also the Dominical Letters in either the Julian (Old Style) or Gregorian (New Style) Calendar. Arranged by JOHN C. ROBERTSON, Kirkcaldy.

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Find in the Table-of-Hundreds the first figure, or figures, of the number of the given year in either the Julian or Gregorian section as required. Next find in the Table-of-Tens-and-Units the last figures. Then find the factor for the year in line with its first and under its last figures. The sum of the factors for the year and the month indicates the required Monthly Table. Factors in heavy type indicate Leap-Years.

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FACTORS FOR

DAYS.

THE MONTHS.

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Factors for Leap

Years=

WHITAKER'S ALMANACK, 1913.

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WEGENER'S "PROFILE OF THE ATMOSPHERE."

The lowest dotted line (about 7 miles above the ground) is "where the air stops growing colder." It is the upper limit of ordinary clouds, of storms, and of balloon ascensions by human beings. Nearly all the moisture of the atmosphere lies below this level. Above this line comes the second layer of the atmosphere, the stratosphere (also called the "isothermal layer," because a thermometer carried up through it would show little change of temperature with change of elevation). This layer has been penetrated by sounding-balloons, carrying meteorological apparatus but no human aeronaut, as far as 20 miles above the earth. At about 50 miles the upper limit of twilight-begins a region in which the atmosphere consists chiefly of hydrogen. Near the lower border of this region clouds of fine dust have sometimes been observed, shining by reflected sunlight on summer nights. These "noctilucent clouds" are commonly explained as the product of volcanic eruptions on the earth (they were frequently seen after the eruption of Krakatoa), but may be of cosmical origin.

Concerning the uppermost regions of the atmosphere we have little positive knowledge. Above about 130 miles from the earth. Dr. Alfred Wegener, the author of this diagram, believes that a gas ("geocoronium"), much lighter than hydrogen prevails, to which he attributes the characteristic green line in the spectrum of the higher auroras. This is hardly more than a guess at present.

CHAPTER III.

METEOROLOGY.*

BY C. FITZHUGH TALMAN.

COMPOSITION, PRESSURE AND HEIGHT OF THE ATMOSPHERE.

At

Up to a height of eight or ten miles above the earth the composition of the atmosphere is remarkably uniform, as to its principal constituents. Pure dry air is a mixture (not a chemical compound) of gases in the following proportions, by volume: Nitrogen, 78.03% oxygen, 20.99%; argon, 0.94% carbon dioxide, 0.03%; hydrogen, 0.01%; together with minute quantities of neon, krypton, xenon, helium, and possibly other gases. the levels habitable by man the air always contains invisible water vapor (from a small trace to about 5%), and usually small and variable amounts of ozone, ammonia, nitric acid, and other gases, which, on account of their irregular occurrence, are not classed among the normal constituents of the atmosphere. Lastly, the lower air always contains solid impurities, in endless variety, generically known as dust.

The pressure of the air at sealevel averages about 14.7 pounds to the square inch, which corresponds to a reading of 29.92 inches of the barometer. The density and the pressure of the air decrease rapidly as we ascend. At an altitude of 3.6 miles above sea-level they are reduced onehalf; i. e., half the whole mass of the atmosphere lies below this elevation; yet the atmosphere extends at least 300 miles above the earth. At great altitudes the tenuity of the atmosphere is comparable to that of the best "vacuums" attainable in the laboratory.

THE UPPER ATMOSPHERE.

The investigation of the upper atmosphere, which has been prosecuted most actively since the beginning of the twentieth century, constitutes a special branch of research known as

*Copyright, 1912, by Munn & Co., Inc.

aerology. It has made meteorology a "science of three dimensions."

The atmosphere is "sounded" by means of meteorological instruments attached to kites and balloons. The greatest height ever attained by a kite was 4.51 miles above sea-level, at Mount Weather, Va., May 5, 1910; by a balloon, 20.14 miles, at Uccle, Belgium, June 9, 1911. Above the levels attainable by these means, the atmosphere is studied by observations of the aurora, meteor trains, and optical phenomena, and by computation of the distribution of the atmospheric gases, as determined by their atomic weights.

Since the year 1902 it has been known that the atmosphere is divided into at least two layers, or shells, having quite different properties. If we could travel in a balloon to the top of the atmosphere we should find the air rapidly growing colder as we ascended, until, at a height of about 7 miles, this fall in temperature suddenly ceased, as we entered the isothermal layer, or stratosphere. air below this level-the tropospherecontains practically all the moisture of the atmosphere;, hence all clouds (except possibly dust clouds of volcanic or cosmical origin). All storms, also, are confined to the troposphere.

The

During our ascent through the stratosphere we should find ourselves in a region of comparatively gentle winds and of uniform temperature in a vertical direction. We should find the atmosphere gradually ceasing to be "air," and becoming mainly nitrogen. Later we should reach a region in which nitrogen was replaced by the lighter gas hydrogen.

Possibly a gas even lighter than hydrogen exists in the atmosphere, and if so it must be most abundant at the highest levels. Its existence is conjectured on the evidence of the spectrum of a certain type of aurora,

and it has been named provisionally "geocoronium."

Wegener's profile of the atmosphere represents these facts graphically.1

THE METEOROLOGICAL ELEMENTS AND

INSTRUMENTS.

The temperature of the air is measured with the thermometer, or continuously with the thermograph. Extremes of temperature are automatically recorded with the maximum and the minimum thermometer. The temperature underground is measured with the soil thermometer.

The total solar radiation or insolation is measured with the actinometer or the pyrheliometer. The intensity of the shorter wave-lengths, including the ultra-violet, is measured with several forms of photometer. The distribution of energy throughout the solar spectrum is measured with Langley's bolometer. The duration of sunshine is measured with the sunshine-recorder.

The pressure of the air is measured with the barometer (mercurial or aneroid), or continuously with the barograph. Minute fluctuations of pressure are measured with the statoscope, the microbarograph, the pressure-variometer, or the variograph. Altitude, as affecting barometric pressure, is measured with the hypsometer.

The humidity of the air (relative or absolute) is measured with the hygrometer or the psychrometer; or continuously with the hygrograph.

The rainfall is measured with the rain-gage-probably the oldest of meteorological instruments. Raingages were used in India in the 4th century B.C. The self-recording raingage makes a continuous record of the amount of rainfall; the ombroscope of its duration only, including the lightest showers. Snowfall is usually measured as rainfall; i. e., the observer melts the snow before measuring it, or else computes its "water equivalent." There are, however, snow-gages of various forms. The drosometer, for measuring dew, is little used.

Wegener's "geocoroniumsphere" is still a matter of speculation, but has attained considerable prominence in the current literature of meteorology. His "hydrogensphere" is, in current terminology, usually included in the stratosphere.

Evaporation is measured with the atmometer (atmidometer, evaporimeter); continuously with the atmograph.

The direction of the wind is observed with the wind-vane, which may be arranged to make a continuous record. The velocity or the force of the wind is measured with the anemometer (continuously with the anemograph), or estimated by the observer in terms of a simple windscale. (See Beaufort Scale at the end of the chapter.) The vertical component of the wind is measured with the vertical anemometer.

The state of the weather, as clear, partly cloudy, cloudy, raining, foggy, etc., is observed non-instrumentally. The degree of cloudiness is the number of tenths of the sky covered with clouds, from 0 cloudless to 10completely overcast. Exact measurements of cloudiness may be made with Besson's nephometer. The duration of cloudiness at night is sometimes measured with the pole-star recorder.

Clouds are observed as to their form, and as to direction and speed of movement, as measured with the nephoscope. Photographic measurements of clouds are made with the photonephograph.

The normal electrical phenomena of the atmosphere include the vertical potential gradient, measured with collectors and electrometers (some selfrecording); also ionization and its effects, observed with dissipation-apparatus, conductivity-apparatus, ioncounters, etc.

Lightning flashes set up Hertzian waves (known to wireless operators as "atmospherics," "strays," "statics," "X's," etc.) and these are recorded at a distance by the ceraunograph, or thunderstorm-recorder, or audibly in the ceraunophone.

Aerological observations, now forming part of the routine of many observatories, have been referred to in the preceding section. The apparatus employed includes the kite and the kite-reel (usually a power-driven winch); the captive balloon; the pilot-balloon (sent aloft without attached instruments, merely for observing the drift of the upper air, and usually followed with a theodolite); the sounding-balloon (which bursts at a great altitude, and is wafted gently to the ground, with its attached instruments. by a parachute

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