ON FORCE. 287 
lio\v a sun might be formed and maintained on known 
thermo-dynamic 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. Jf 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 dimin- 
