NATURAL PHILOSOPHY. 153 



not further the attainment of his object. He does not want his ax! is 

 heated, and thence he avoids as much as possible expending his power 

 in heating them, in fact he lias obtained his force f'roni heat, and it 

 is not his object to reconvert the force thus obtained into its primitive 

 form. For by every degree of temperature generated by the friction 

 of his axle, a definite amount would be withdrawn from the urging 

 fbrc-e of his engine. There is no force lost absolutely. Could we 

 g.tiher up all the heat generated by the friction, and could we apply it 

 mechanically, we should by it be able to impart to the train the precise 

 amount of speed which it lost by the friction. Thus every one of 

 thufC railway porters whom you see moving about with his can of 

 yeiiow grease, and opening the little boxes which surround the car- 

 nage axles, is, without knowing it, illustrating a principle which forms 

 the very solder of nature. In so doing he is unconsciously affirming 

 both the convertibility and the indestructibility of force, lie is prac- 

 tically asserting that mechanical energy may be converted into heat, 

 and that when so converted it cannot still exist as mechanical energy, 

 but that for every degree of heat developed, a strict and proportional 

 equivalent of locomotive force of the engine disappears. A station 

 is approached say at the rate of oO or 40 miles an hour ; the brake is 

 applied, and smoke and sparks issue from the wheel on which it 

 presses. The train is brought to rest; how? Simply by converting 

 the entire moving force* which it possessed at the moment the brake 

 was applied, into heat." 



THE COOLING OF THE EARTH AND ITS CONSEQUENCES, BY DR. 



J. R. MAYER. 



If we assume that our globe was once in an incandescent state (as 

 is now generally admitted), it must have lost heat at first at a very 

 rapid rate ; gradually this process became slower ; and although it has 

 not yet entirely ceased, the rate of cooling must have diminished to a 

 comparatively small magnitude. 



1 \vo phenomena are caused by the cooling of the earth, which on 

 account of their common origin are intimately related. The de- 

 crease of temperature, and consequent contraction of the earth's crust, 

 must have caused frequent disturbances and revolutions on its surface, 

 accompanied by the ejection of molten masses and the formation of 

 protuberances : on the other hand, according to the laws of mechan- 

 ics, the velocity of rotation must have increased with the diminution 

 of the volume of the sphere, or in other words, the cooling of the earth 

 must have shortened ihe length of the day. As the intensity of such 

 disturbance and the velocity of rotation are closely connected, it is 

 clear that the youth of our planet must have been characterized by 

 continual violent transformations of its crust and a perceptible accelera- 

 tion of the velocity of its axial rotation ; while in the present time the 

 metamorphoses of its surface are much slower, and the acceleration of 

 its axial revolution diminished to a very small amount. 



If we imagine the times when the Alps, the chain of the Andes, and 

 the Peak of Teneriffe were upheaved from the deep, and compare 

 with such changes the earthquakes and volcanic eruptions of historic 

 times, we perceive in these modern transformations but weak images 

 of t..e analogous processes of bygone ages. 



