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The following ready, though sufficiently accurate, methods are useful: First-Deduct 3 per cent from the Moslem years, add to the answer 622. Thus, taking the year of the Hegira, 1328: Three per cent to be deducted gives 40; 40 from 1528 leaves 1273; then add (22, and that makes 1910.

Second-Multiply 970,224 by the year of the Hegira, cut off six decimals from the product and add 21.5774. The sum will be the year of the Christian Era, and the day of the year will be found by multiplying the decimal figures by 365. The result Day sometimes differ a day from the truth, as the intercalery days do not occur simultaneously; but as the day of the week can always be accurately obtained from other tables the error, if any, can be readily adjusted. Example: Required, the date on which the year 1362 of the Hegira begins: 970,224×1,362 1,321.445088 (after cutting off six decimals). To this add 621.5774-1,943.0225. The decimal multiplied by 365 gives 8. Thus the date is the 8th day, or Eth day of January, of the year 1943. From other tables it is known that January 8, 1943, falls on a Friday.


Distance and Size.-The sun's mean distance from the earth (always reckoned from centre to centre) is 92,885,000 miles, with a variation between January 1 and July 3 of 3,100,000 miles, owing to the ellipticity of the earth's orbit. The diameter of the sun or the length of the line passing through its centre from one side to the other is 7,000 miles. If a railroad were laid round the sun a train moving seventy miles an our would take five years, without intermission, to make the journey. A journey Around the earth at the same rate would take only a fortnight.

Weight. The sun weighs 330,000 times as much as the earth. But, bulk for balk, thirteen million earths would go to make up one sun. It follows from this that the matter composing the sun must on an average be about one-fortieth as dense the matter composing the earth, or less than one-seventh as dense as water; so it may be fairly concluded that the sun is a gaseous body.

Heat.-It has been calculated that the heat thrown on a square mile exposed noon under the equator would melt in an hour 26,000 tons of ice. This amount bas to be multiplied fifty million times to arrive at the quantity of heat received the earth's surface during a single hour. Yet this (normous supply is even than one two-thousand-millionth part of what the sun pours forth in all directions in space.

There are various theories to account for the enormous store of heat and light in the sun. The theory now generally accepted by physicists is that the gradual contraction of the solar orb in cooling is the chief source of the sun's apparent inexhaustible energy. It has been calculated that at the present rate of expenditure of heat the sun's diameter would contract four miles in a century, and in a few millions of years it may become as dense as the earth.

The sun is composed of very much the same materials as the earth, except that they are at a much higher temperature. About forty of the seventy terresal elements have been identified by the spectroscope as existing in the vapors

around the sun. stances not already known. Astronomers think that they find traces there of very few subEven these may be discovered on the earth some day. Motion.-The sun revolves on its axis in about twenty-two days: but apparently It takes two days longer than this, owing to our own globe's motion in its orbit. This eriod of revolution has been computed from observation of sunspots, it having en noted that a certain spot, vanishing at one edge of the solar disk-or "dispearing 'round the corner," as one may say-returns to the same position in the period named. The other real motion of the sun is the almost imperceptible

through space, in which "grand march" the members of the solar system company him earth, moon, planets, planetoids and some comets. Lovement is directed is still a subject of discussion

Whence this


moon from earth's

Distance and Velocity. The greatest distance of the distance from earth's surface 217,740 miles. tre is 252.600 miles, its least distance from earth's centre 221,700 miles, its least It travels in its orbit with a velocity of 134 feet a is 10 miles an hour. Sidereal and Synodic Revolutions of the Moon.-When the moon, after passBake a sidereal revolution. a star, completes a revolution so as to come back to the same star, it is said to the sun the mean duration of the lunar month, that is nutes and 11.46 seconds, but owing to her motion in common with the earth around time for this is 27 days 7 hours 43

the time between successive which is called the synodic revolution. moons is a little longer, i. e., 29 days 12 hours 44 minutes and 2.87 seconds,

orbit is approximately an ellipse whose two es are nearly of equal length, but an ellipse will represent its orbit for a very hort time. Owing to the inclination of the earth's equator to the ecliptic, the moon sometimes seen, at the full, coursing along a circle which passes near the zenith these latitudes and sometimes, in the same phase, along an arc low down in the thern

n's orbit to the plane of the ecliptic, amounting to 5° 8', so that during one-half of her orbalt she is soune off the sun's annual path and during the remaining half 5th of it. The points where she crosses the ecliptic are known as her nodes. Rotation. The moon's rotation on its axis agrees in period with its revolu on around the earth, so that we have always the same side presented to our view.

Occasionally, however, we see a little around one or the other edge. This phenomenon is known as libration in longitude.

Phases. The moon's changes in shape from a crescent to a full disc are due conjointly to the globular form of the moon, its motion and the fact that it does not shine by its native light, but simply reflects the solar rays. The illuminated (or convex) edge of its figure is always turned toward the sun. When right opposite the sun it appears as full, and sometimes is so situated as to be partially obscured by the earth's shadow. When it is near the sun in the sky it appears as a thin crescent, turning almost entirely its dark side to the earth. Sometimes, at new moon, it comes between us and the sun, obscuring his disc either in a partial or total eclipse. At either half moon the moon is said to be in its quadrature, or in the "first" or "last quarter." At new and full moon it is said to be in syzygy (Greek syn, "together"; zygon, "yoke''). These changes result from the constant darkness of one side of the moon, and constant brightness of the other, the crescent being larger or smaller as, from the moon's change of position, more or less of the bright side is seen from the


Eclipses. Whenever the earth gets between the moon and the sun, cutting off the light of the latter, a so-called eclipse of the moon takes place. An eclipse of the moon occurs only at full moon. During a lunar cycle there will be, on the average, twenty-nine eclipses of the moon.

The Harvest Moon.-If the plane of the moon's orbit coincided with that of the earth's equator, the moon would rise about fifty minutes later each day, but owing to the inclination between these planes to one another this retardation is quite different at different times. This retardation may be reduced to nothing when in the northern latitude full moon occurs near the autumnal equinox, so that for several nights the full moon rises about the same time soon after sunset. At or about the time of harvest in the northern temperate zone the sun in its annual course is approaching the celestial equator, which it crosses from north to south on September 22. On that date it sets close to the exact western point of the horizon. If it happens to be also full moon, the moon rises that evening as the sun sets, or close to the exact eastern point of the horizon. Thus it begins to give light at sunset, and continues to do so until sunrise, when it sets opposite the sun, just as the latter rises. This arrangement holds good without any great change for several days, so that there is practically no darkness, especially if the weather is fine. The full moon which thus illumines the autumn night is called the harvest moon. The hunter's moon is the next full moon after the harvest moon; the same phenomenon, less marked, occurs.

Tides. The chief cause of the tides is the attraction of the moon, which, affecting most strongly the side of the earth nearest to it, draws or heaps up the waters in the parts of the earth successively turned toward it. At the same time the moon attracts the bulk of the earth, and, as it were, pulls the earth away from the water on the surface furthest from it, so that here also the water is raised, although not quite so much as on the nearer side. The waters being thus heaped up at the same time in these two parts of the earth, and the waters situated half way between them being thus necessarily depressed, two high and low tides occur in the period of a little more than one revolution of the earth on its axis. When the sun and moon are in conjunction or opposition, at times of new and full moon, their tidal waves will be superposed crest upon crest, and the effect will be what is called 'spring tide"; when they are in quadrature the lunar tide will be partially neutralized by the solar tide, and the result will be a "neap tide."

Size, Volume, Mass, Density. The moon's diameter is 2,163 miles, a little more than a quarter of the earth's. Its surface is therefore 0.074 of the earth's, or, in square miles, about 14,657,402. The earth taken as a unit, the moon's density is 0.63; mass, 1/80, volume 1/50: that is to say, it would require the materials of 80 moons to form our globe; the earth is 50 times larger than the moon and its density is in the ratio of 10 to 16. Its smaller size and mass cause gravity to be only of the terrestrial attraction; the same exertion which would lift a given weight here would raise a weight six times as great there, and a body instead of falling 16 feet in the first second would fall only 2% feet.

Light, Temperature.-Like the earth, the moon has no light of its own, but receives all from the sun, and its day-the interval from sunrise to sunrise--is a month. At full moon it sends to us about 1-600,000 part of the light given by the midday sun.

Physical Conditions, as Seen Through the Telescope.-The surface of the moon is totally unlike that of our earth. All the details are hard, cold and glaring in their delineations. All are marked in white and black or in various shades of yellowish gray. Nothing like mist, cloud or water has ever been seen. The so-called seas on the moon are simply portions of the surface darker in color than the average and very much broken up by craters and mountain ranges. Nor is there any evidence of an atmosphere. Observation of the stars suddenly occulted by the moon, as well as the spectroscope, confirms this, and if there be even an attenuated atmosphere it cannot have more than 1/200 of the surface density of our own. In consequence there is no vegetation, no life. The mountain ranges, called the lunar Alps, Appenines, Cordilleras, etc., range from 20,000 feet in height downward; the lunar rills, clefts or cracks in the surface pass often right through mountains and valleys, sometimes for a distance of 300 miles, their breadth being relatively so small as to give them the appearance of true cracks. The whole aspect suggests volcanic action on the lunar surface in remote ages, but nothing like an active volcano has ever been seen.

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The total area of the earth is about 197,000,000 square miles, and its total population 1,626,000,000. The area of the water of the earth is about 145,000,000 square iles. The area of the land of the earth is about 52,000,000 square miles. The largest continents are:




North America..

South America.


The area occupied by the water is:







Inland waters..

British Empire..

Russian Empire.



Caited States..


Turkish Empire......

sslan Empire.

tited States.


German Empire..

apan and Corea.

[25,000,000 sq. miles
70,000,000 sq. miles)
(22,500,000 sq. miles

4,000,000 sq. miles]
7,500,000 sq. miles
16,000,000 sq. miles

1. London

2 New York.

3. Paris

'The figures of population, excepting those for the United States, are taken from The Year Book of the Bureau des Longitudes. Including all islands in the Eastern Indian and Southern Pacific oceans. Including population in the Dutch East Indies. The largest states, comprising parent country and colonies or possessions, are:

4. Tokio

1. Chicago

.11,467,294 sq. miles

8,647,657 sq. miles)
4,277,170 sq. miles)
4,279,130 sq. miles)
3,756,884 sq. miles
3,218,991 sq. miles
1,157,860 sq. miles

The largest cities in the world are:

Sorth America.

uth America.

urope Ta rica beania stralia

in Square Miles.


7,500,000 3,800,000 4,700,000

The highest mountains in the world are:


According to the number of inhabitants, the countries range as follows: British Empire and Colonies....403,000,000 Austria-Hungary


Greatest Depth

(Murray-Challenger Expedition).

27,366 feet
30,000 feet
18,582 feet

9,000 feet 25,200 feet

Germany (with German

Argentine Republic..
Belgium and the Congo

.350,000,000 Netherlands

.152,000,000] [Turkey

98,000,000 [Italy

81,000,000 Belgium and the Congo.
78,000,000 [Spain

.7,429,740 6. Berlin

4,766,883 7.


2,763,393 8. St. Petersburg..


9. .2,185,283 10.

Number of Inhabitants.

851,000,000 170,000,000



437,000,000 51,000,000

Name of Mountain.
Mt. McKinley, Alaska..
Aconcagua, Chili....
Elbrooz, Caucasus, Russia.
Mt. Everest, Himalaya, India.
Kilimandjaro, East Africa..
Mt. Hercules, North New Guinea.

1,140,290 sq. miles 1,135,840 sq. miles

921,027 sq. miles 838,442 sq. miles 736,400 sq. miles

50,000,000 44,000,000 38,000,000

36,000,000 27,000,000 20,000,000




.1,549,008 .1,359,254


20,464 feet 23.080 feet

18,526 feet

29,002 feet 20,065 feet

32.768 feet 7,167 feet

The longest rivers in the

world are: In Europe, Volga, about 2,200 miles; in

sa, Yenisei, about 2,700-3,000 miles, and Yang-tse-Kiang, about 3,000; in Africa, e, about 3,240 miles; in North America, Mississippi and Missouri, 4,300 miles; in th America, Amazon and Beni, 4,000 miles; in Australia, Darling, more than 2,345


The largest lake in the world is Lake Superior. It covers an area of 31,200 square Me and has a mean depth of about 475 feet.

The greatest cataract in the world, surpassing by far Niagara and Zambezi Falls, the Ignazu River, which partly separates Brazil from Argentina, one thousand sby boat from the nearest settlement. The precipice over which the river plunges 210 feet high, that of Niagara being 167 feet. The cataract is 13,123 feet wide, or at two and a half times as wide as Niagara. It is estimated that 100,000,000 tons water passes over Niagara in an hour; a like estimate gives the Falls of Ignazu 400,000 tons.


The oldest city in the world is Damascus, in Syria. The exact date of the foundof this city, once so famous for its manufacture of silks, jewelry and blades, is

not known, but it is said to have been begun by a greatgrandson of Noah, and probably is 4,200 years old. Next comes Athens, the capital of Greece, which is about 3.453 years old-older than any other European city. Peking, the capital of China, is said to be about 3,000 years old. Jerusalem, which was a Jebusite city in the days of Abraham, is 3,000 years old at least.

The coldest country in the world is Werchojansk, in Siberia, longitude 133 degrees 51 minutes east, latitude 67 degrees 34 minutes north, where a lowest temperature of minus 90 degrees Fahrenheit has been observed, and the mean of January is minus 48 degrees Fahrenheit. The country is inhabited by about one hundred and five thousand persons of the Jakut and Lamat races.


The history of the earth is divided into five eras with corresponding rock systems: 1, Archaean or Eozoic (dawn of life), embodied in the Laurentian system; 2, Palaeozoic (old life), embodied in the Palaeozoic or primary system; 3. Mesozoic (middle life), recorded in the secondary system; 4. Cenozoic (present life), recorded in the Tertiary and Quaternary systems, and 5, the Psychozoic (Era of the Mind), recorded in the recent system. These grand divisions, with the exception of the last, are founded on an almost universal unconformity of the soil.

The history of the earth is otherwise divided into Seven Ages, founded on the culmination of certain great classes of organisms. These are:


1. The Archaean or Eozoic Age, represented by the Laurentian system of rocks. 2. The Age of Mollusks, represented by the Silurian series of rocks. The Age of Fishes, represented by the Devonian rocks. 4. The Age of Acrogens, or sometimes called the Amphibian, represented by the Carboniferous rocks. The Age of Reptiles, represented by the secondary rocks. 6. The Age of Mammals, by the Tertiary and Quatenary, and 7. The Age of Man, by the recent rocks. The diagram shows how the ages correspond with the eras:



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[The vertical height represents tirae, the strong horizontal lines separate the ages, the shaded spaces represent the origin of the dominant classes of animals and plants. Thus, for instance, the class of reptiles commenced in the time of Carboniferous rocks.]

The subdivisions of eras and ages into periods and epochs are founded on less nonconformity in the rock system, and less conspicuous changes in the life system. The names and periods are often, and of epochs are nearly always, local,

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and therefore different in different countries. The table represents, as far as periods, the classification used in America.

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The total thickness of all the strata known amounts to 72.000 metres (44.74 miles), of which about 1,000 metres belong to the Cenozoic (recent life) era, 3,000 to the Mesozoic (middle life), 30,000 to the Palaeozoic (old life), and 38,000 to the Eozoic (dawn of life) eras. From these figures the approximate relative duration of the eras is calculated.



In a publication issued in July, 1910, by the Smithsonian Institution, the age of the earth was estimated by Frank Wigglesworth Clarke and George F. Becker, of the Geological Survey, as "not above seventy million or below fifty-five million years." The age of the earth always has been a subject for discussion among men of science, and largely without any definite agreement among the representatives of the different branches of studies on account of the different points of approach. The more recent discussions as to the earth's age have placed the time as follows: Lord Kelvin, in 1862, 20,000,000 to 400,000,000 years, with a probable 98,000.000 years; in 1897 Lord Kelvin revised his figures to 20,000,000 to 40,000,000 years; Clarence King and Carl Varus, in 1893, 24,000,000 years: De Lapparent, in 1890, 67,000,000 to 90,000,000 years; Charles D. Walcott, secretary of the Smithsonian Institution, in 1893, maximum age, 70,000,000 years; J. Joly, in 1899, age of the ocean, 80,000,000 to 90,000,000 years, and W. J. Sollas, in 1909, age of the ocean, 80,000,000 to 150,000,000 years.


While from the researches of the physiologist, the anatomist, the philologist and the psychologist the same testimony is obtained as to the specific unity of the human race, ethnology for convenient classification divides men, according to their physical or psychical characteristics, into groups, families, clans, tribes, and, on account of their distribution, these are sometimes named for geographical divisions. In these efforts of classification different schemes have been tried. Linnæus classifies the races according to geographical areas. Dall divides men Into three groups: white, black and yellow; Garland, into six races, separating the Dravidians from the other groups. The cranological school founded by the elder Retzius made the shape of the head the basis of classification, and accordingly mankind was divided into long skulled and short, broad skulled races. Blumenthal gives five groups, classified according to the color of the skin. Professor Huxley also designated five groups along somewhat similar lines. Morton used the skull as a basis of classification; Haeckel and Broca the hair, and Hale language. The tendency now seems to be to return to the earlier classification and its three greater subdivisions white, black and yellow, or Caucasian, Negro and Mongolian, with the addition of two more subdivisions, red and brown, or American and Malay. Under such plan Blumenthal's scheme of dividing men according to the color of the skin can be used. Under it there are grouped: (1) Caucasian, or white; (2) Ethiopian, or black; (3) Mongolian, or yellow; (4)

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