ON FORCE. 28? 



how a sun might be formed and maintained on known 

 thermo-dyuamic principles. 



Our earth moves in its orbit with a velocity of 

 68,040 miles an hour. Were this motion stopped, an 

 amount of heat would be developed sufficient to raise the 

 temperature of a globe of lead of the same size as the 

 earth 384,000 degrees of the centigrade thermometer. 

 It has been prophesied that " the elements shall melt with 

 fervent heat/' The earth's own motion embraces the con- 

 ditions of fulfillment; stop that motion and the greater 

 part, if not the whole, of our planet would be reduced to 

 vapor. If the earth fell into the sun, the amount of heat 

 developed by the shock would be equal to that developed 

 by the combustion of a mass of solid coal 6,435 times the 

 earth in size. 



There is one other consideration connected with the per- 

 manence of our present terrestrial conditions, which is 

 well worthy of our attention. Standing upon one of the 

 London bridges, we observe the current of the Thames 

 reversed, and the water poured upward twice a day. The 

 water thus moved rubs against the river's bed, and heat is 

 the consequence of this friction. The heat thus generated 

 is in part radiated into space and lost, as far as the earth is 

 concerned. What supplies this incessant loss? The earth's 

 rotation. Let us look a little more closely at the matter. 

 Imagine the moon fixed, and the earth turning like a 

 wheel from west to east in its diurnal rotation. Suppose a 

 high mountain on the earth's surface approaching the 

 earth's meridian; that mountain is, as it were, laid hold of 

 by the moon; it forms a kind of handle by which the earth 

 is pulled more quickly round. But when the meridian is 

 passed the pull of the moon on the mountain would be in 

 the opposite direction, it would tend to diminish the ve- 

 locity of rotation as much as it previously augmented it; 

 thus the action of all fixed bodies on the earth's surface is 

 neutralized. But suppose the mountain to lie always to the 

 east of the moon's meridian, the pull then would be always 

 exerted against the earth's rotation, the velocity of which 

 would be diminished in a degree corresponding to the 

 strength of the pull. Tlie tidal wave occupies this position 

 it lies always to the east of the moon's meridian. The 

 waters of the ocean are in part dragged as a brake along 

 the surface of the earth; and as a brake they must dirniu- 



