180 ON THE OEIGIN OF THE PLANETAEY SYSTEM. 



If a weight falls from a height and strikes the 

 ground its mass loses, indeed, the visible motion which 

 it had as a whole in fact, however, this motion is not 

 lost; it is transferred to the smallest elementary 

 particles of the mass, and this invisible vibration of 

 the molecules is the motion of heat. Visible motion 

 is transformed by impact, into the motion of heat. 



That which holds in this respect for gravity, holds 

 also for gravitation, A heavy mass, of whatever kind, 

 which is suspended in space separated from another 

 heavy mass, represents a force capable of work. For 

 both masses attract each other, and, if unrestrained by 

 centrifugal force, they move towards each other under 

 the influence of this attraction ; this takes place with 

 ever-increasing velocity ; and if this velocity is finally 

 destroyed, whether this be suddenly, by collision, or 

 gradually, by the friction of movable parts, it develops 

 the corresponding quantity of the motion of heat, the 

 amount of which can be calculated from the equiva- 

 lence, previously established, between heat and me- 

 chanical work. 



Now we may assume with great probability that 

 very many more meteors fall upon the sun than upon 

 the earth, and with greater velocity, too, and therefore 

 give more heat. Yet the hypothesis, that the entire 

 amount of the sun's heat which is continually lost by 

 radiation, is made up by the 'fall of meteors, a hypothesis 



