4'20 Dr. J. R>. Mayer on Celestial Dynamics. 



motion or rest. Change — that is to say, transition from one 

 state of things to another — alone requires and admits of expla- 

 nation." 



It is evident that this reflection is not fitted to suppress the 

 desire for an explanation of the phenomenon in question. As all 

 matter has the tendency to assume the same temperature as 

 that possessed by the substances by which it happens to be 

 surrounded, and to remain in a quiescent state as soon as equi- 

 librium has been established, we must conclude that, whenever 

 we meet with a body warmer than its neighbours, such body 

 must have received at a (relatively speaking) not far distant 

 time, a certain degree of heat, — a process which certainly allows 

 of, and requires explanation. 



Newton's theory of gravitation, whilst it enables us to de- 

 termine, from its present form, the earth's state of aggregation 

 in ages past, at the same time points out to us a source of heat 

 powerful enough to produce such a state of aggregation, power- 

 ful enough to melt worlds; it teaches us to consider the molten 

 state of a planet as the result of the mechanical union of cos- 

 mical masses, and thus to derive the radiation of the sun and 

 the heat in the bowels of the earth from a common origin. 



The rotatory effect of the earth also may be readily explained 

 by the collision of its constituent parts ; and we must accord- 

 ingly subtract the vis viva of the axial rotation from the whole 

 effect of the collision and mechanical combination, in order to 

 obtain the quantity of heat generated. The rotatory effect, 

 however, is only a small quantity in comparison with the in- 

 terior heat of the earth. It amounts to about 4400 xT kilo- 

 grammetres, T being the weight of the earth in kilogrammes, 

 which is equivalent to 12 xT units of heat, if we assume the 

 density of the earth to be uniform throughout. 



If w r e imagine the moon in the course of time, either in con- 

 sequence of the action of a resisting medium or from some 

 other cause, to unite herself with our earth, two principal effects 

 are to be discerned. A result of the collision would be, that the 

 whole mass of the moon and the cold crust of the earth would 

 be raised some thousands of degrees in temperature, and con- 

 sequently the surface of the earth would be converted into a 

 fiery ocean. At the same time the velocity of the earth's 

 axial rotation would be somewhat accelerated, and the position 

 of its axis with regard to the heavens, and to its own surface, 

 slightly altered. If the earth had been a cold body without 

 axial rotation, the process of its combining with the moon 

 would have imparted to it both heat and rotation. 



It is probable that such processes of combination between 

 different parts of our globe may have repeatedly happened 



