EARTH 



1904 



EARTH 



of about nineteen miles per second; so smooth 

 is the motion through space and so slight are 

 the variations of the earth's surface in pro- 

 portion to its mass that no billiard ball has 

 ever yet been made with less proportionate 

 deviation from perfectly "true" motion. 



The earth is nearest to the sun when it is 

 winter in the northern hemisphere; when it is 

 summer, farthest away from it. This at first 

 appears improbable, yet it is true. It is not 

 the distance from the sun that produces cold ; 

 the oblique direction of the sun's rays in win- 

 ter, due to inclination of the earth's axis, pre- 

 vents the radiation of heat over the northern 

 surface. From the earth it appears as though 

 the sun were also describing a similar circular 

 path through the heavens. Hence it is that 

 one group of stars is found near the sun at 

 one time, and another group is near it at 

 another date. The earth's position and point 

 of view have changed, however, for the sun 

 remains stationary. 



Daily Rotation of the Earth. In 23 hours, 56 

 minutes, 4.1 seconds the earth makes a complete 

 rotation on its own axis, this axis being in- 

 clined to the plane of its path about the sun 

 at an angle of 23%. In this rotation on the 

 axis a person at either Pole would not move, 

 but at the equator he would be whirled safely 

 through space at the rate of about 1,000 miles 

 per hour, for the equatorial circumference is 

 nearly 25,000 miles. The motion of the earth 

 causes the sun apparently to rise towards the 

 North Pole from March 21 to June 21, until it 

 is 23% above the equator; to descend towards 

 the equator from June 21 to September 21 ; 

 then it commences to sink toward the South 

 Pole, and to return to the equator about March 

 21, the vernal equinox. 



This apparent motion of the sun, in reality 

 the motion of the earth, is the cause of the 

 changes in seasons, the lengths of day and 

 night and the rising and setting of the sun. 

 Countries lying north or south of the equator 

 have equal days and nights twice a year, at the 

 equinox. The earth is divided by imaginary 

 lines into climatic zones, or regions. Within 

 the limits of 23% of the North and South 

 poles are the Arctic and Antarctic circles; 

 within 23% on each side of the equator lie 

 the tropics of Cancer and Capricorn, embrac- 

 ing the torrid zone. Between the tropics and 

 the polar circles lie the north and south tem- 

 perate zones, the area of the world's culture 

 and the theater wherein all man's greatness 

 has been achieved. 



The Earth as a Clock. No mechanical ap- 

 pliance for time-keeping has yet been invented 

 which can compete with the earth in the unfail- 

 ing regularity of its motions. Although the 

 earth is subject to influence of gravity from the 

 other planets which might cause variation, such 

 a change has never been noted to any appre- 

 ciable extent, and it would take probably more 

 than twenty centuries to alter the time-keeping 

 qualities of the earth sufficiently to attain a 

 result capable of expression in fractions 'of a 

 socond. Such is the poetic "harmony of the 

 spheres." 



At exactly the noon hour, when the sun is 

 on the meridian at Greenwich Observatory, 

 the time is flashed all over Europe; in Wash- 

 ington the time ball falls at the instant of 

 noon from the tower of the naval observatory, 

 and the telegraph announces the time. 



Magnetism. One of the most striking 

 features presented by the earth as a whole is 

 its magnetism. The earth is one huge magnet 

 and has two magnetic poles, which, although 

 near the geographical poles, do not coincide 

 with them. The north magnetic pole was lo- 

 cated in 1905. The action of the earth as a 

 magnet is seen when a magnetic needle, bal- 

 anced on a point, remains in one position, 

 pointing nearly due north and south. On this 

 principle the compass, which renders world 

 navigation possible, is based. 



Some Computations. Scientists agree quite 

 well, in spite of the immensity of their task, 

 on certain mathematical facts relating to the 

 earth. The circumference and diameter are 

 known and measured with astronomical instru- 

 ments to within less than one-fourth of a mile. 

 One proof that the earth is slightly flattened 

 at the poles is that at Edinburgh, Scotland, a 

 degree is longer than in the vicinity of Madras. 



Diameter of earth at equator (miles) ...7,926.592 

 Diameter through the poles (miles) . . . .7,899.739 



Circumference at equator (miles) 24,899.00 



Area of land surface (square 



miles) 55,641,102. 



Area of oceans and seas (square 



miles) 141,333,882. 



Total of the earth's surface 



(square miles) 196,974,984. 



Weight of earth and at- 

 mosphere (tons) ..3,333,112,909,800,000,000. 

 Proportionate density of water and solid 



matter 1 to 5.5 



Nearest approach to the sun 



(miles) 89,897,000. 



Farthest distance from the sun 



(miles) 92,963,000. 



Length of a degree ofMatitude at 



poles (miles) 69.407 



