centre, we should encounter stupendous difficulties of heat and pressure. ft 

 has been estimated that the temperature of molten lava ranges from 1200 to 

 2000 degrees, Centigrade, and it has also been estimated that at the Earth's 

 centre the density may be as great as ten times that of water, resembling some 

 very heavy metal. Therefore, it is improbable that during the present century 

 we shall begin any tunnel to the terrestrial centre, although the time may be 

 at hand when we shall sink deep shafts to tap and utilize the heat and other 

 energies now hidden beneath our World's surface. 



There is, however, an interesting fact about a shaft sunk from the surface 

 to the centre of the Earth. As we all well know, each of us possesses what is 

 called "weight," due to the attraction between the Earth and our body. For 

 example, one of us weighs "ISO pounds" at the Earth's surface. If this indi- 

 vidual could be weighed at the Sun's surface, he would weigh more than two 

 tons! If at the moon's, only 25 pounds. The reason for this difference in 

 weight Is, that surface gravity varies according to the respective weight and 

 size of the Earth, Sun and Moon. Moreover, a man weighs "ISO pounds" in 

 one region of the Earth, and slightly less than that on the equator. Inasmuch 

 as at the equator the entire centrifugal force Is pulling against the force of 

 gravity- If a shaft could be sunk to the terrestrial centre, and a man weigh- 

 ing "ISO pounds" should be lowered within It, this man would weigh only "112^ 

 pounds" at about 1000 miles below the surface. That is, he would lose one- 

 quarter of his weight after descending one-quarter of the distance to the cen- 

 tre. Then, after descending one-half of the distance to the Earth's centre, he 

 would weigh only one-half of "ISO pounds." If this man reached the very cen- 

 tre of the Earth, he would have no weight at all. The explanation for such 

 losses in weight is that at the terrestrial surface this man Is drawn towards 

 the terrestrial centre by full gravitatlve attraction, whereas, as he descends be- 

 low the Earth's surface. It is as though he were standing upon the surface of a 

 smaller Earth, which would shrink, in size and decrease in gravitatlve attrac- 

 tion in proportion as he approaches its centre. Accordingly, If this man could 

 reach the exact centre of our Earth, there would then exist, no more gravita- 

 tional units to attract his body. Surrounded by a terrestrial sphere approximat- 

 ing 260 billion cubic miles, his surface "weight" of ISO pounds would become 

 a veritable cipher. 



Nevertheless, although this man at the terrestrial centre has no weight him- 

 self, the Earth all around him has a stupendous weight. The man who once 

 weighed "ISO pounds," would be surrounded by a vast sphere, averaging a ra- 

 dius of 39S9 miles In every direction. Inasmuch as the diameter of the Moon is 

 only 2163 miles. It is evident that he could be surrounded by a number of such 

 moons, each moon being eciuldistant about 898 miles from both the Earth's cen- 

 tre and surface . Therefore, It should not cause any surprise that the Earth 

 Is 49 times as large as Its satellite the Moon. However, the weight of our Earth 

 may cause some surprise— 6,000,000,000.000,000,000,000 tons!_ Of course this is 

 a mere cipher compared with the weight of the Sun, but, If we multiply this 

 weight by 2000, or the number of pounds in a ton, we find that the Earth's 

 weight approximates 12 septillion pounds. Possessing such a comparatively 

 stupendous weight, our planet Is able to chain us securely to its surface, and if 

 we try to escape from that surface It ofttlmes dashes us violently to the ground. 

 The Influence of Its mighty mass Is seen alike In a body's falling 16 feet during 

 the first second, 64 feet during the first two seconds, and In the fact that, to 

 escape forever from its surface, a body must rise with a velocity of not less 

 than 37,000 feet per second. 



The Earth's 12 septlUIons of pounds are contained within a vast sphere 

 possessing a bulk of about 260 billion cubic miles. Enclosing this vast sphere, 

 there Is a surface-area approximately 197,000,000 square miles. Upon this wide 

 surface-area there dwell about 1,700,000,000 people, which would be an aver- 

 age of more than 8 people for each square mile of total surface, an average of 

 about 30 for each square mile of land surface, and an average of about S61 peo- 

 ple for each square mile occupied by the United States. Today the density of 

 population In our 48 states averages about 3S citizens, per square mile, from 

 the District of Columbia, which has more than 5,S00 inhabitants in a square 



