78 LIFE AND DEATH. 



Between these phases comes the intermediary phase 

 of which we say that it is a period of virtual or poten- 

 tial energy. This is a way of remembering in some 

 measure the preceding phenomenon i.e., the work of 

 lifting up, and of indicating the phenomena which will 

 follow i.e., the work of the fall. And thus we connect 

 by our thoughts the present situation with the ante- 

 cedent and with the consequent position, and it is 

 from this consideration of continuity alone that the 

 conception of energy springs that is to say, of some- 

 thing which is conserved and is found to be permanent 

 in the succession of phenomena. This energy of 

 which we lose no trace does not appear to us new 

 when it is manifested. Our imagination eventually 

 materializes the idea of it. We follow it as a real 

 thing, having an objective existence, which is asleep 

 during the latent potential period, and is revealed or 

 manifested later. 



Among other examples, that of the coiled spring 

 which is unwound is particularly suitable for show- 

 ing this fundamental character of the idea of 

 mechanical energy, an idea which is the clearest 

 of all. Machines are only transformers and not 

 creators of mechanical energy. They only change 

 one form into another. 



*"" In the same way, too, a stream of water or the 

 torrent of a mountainous region may be utilized for 

 setting in motion the wheels and the turbines of the 

 factories situated in the valley. Its descent produces 

 the mechanical work which would be a creation ex 

 nihilo if we do not connect the phenomenon with its 

 antecedents. We look on it as a simple restitution, if 

 we think of the origin of this water which has been 

 transported and lifted in some way to its level by the 



