66 THE BEGINNINGS OF LIFE. 



particles. If we suppose a wooden ball to be allowed to 

 drop from a moderate height from the raised hand of an 

 experimenter into a basin of water, we have no difficulty 

 in imagining what the result would be. A great splash- 

 ing of the water would occur, and a visible motion of the 

 contents of the basin would remain for a considerable 

 time though gradually diminishing in extent, and 

 therefore in the ease with which it could be perceived. 

 Here the motion of one mass becomes arrested, but 

 communicates itself in a more diffused manner to a 

 mass of water, the visible motion of which is seen to 

 diminish most gradually. But if the ball had been 

 allowed to fall from a height of three hundred feet, 

 instead of from a height of six feet, and if it had fallen 

 upon a solid floor instead of into a basin of water, then 

 (with the exception of the motion of the rebound) all 

 the force existing as visible motion would have been 

 much more immediately expended in the production of 

 molecular motion in the ball and in the floor, and 

 this would have given rise to heat, recognizable by 

 the aid of a thermoscope. Now the motion of a mass 

 is only the motion of an aggregate of molecules the 

 molecules being numerous in direct proportion to the 

 size of the mass. So that in this case also, when the 

 mechanical energy resulting from molar motion is con- 

 verted into heat, the energy (or motion) which the mass 

 displays ceases to manifest itself to us as motion as 

 soon as it has become expended in the production of 

 vibrations in the particles of the bodies which may 



