178 DISCOVERY OH. 



A corollary upon the doctrine of the indestructibility 

 of matter is that an atom may in its time play many 

 parts. When Shakespeare made Hamlet say : 



Imperial Caesar, dead and turned to clay, 

 Might stop a hole to keep the wind away, 



he was only expressing the belief in transmigration held 

 by Empedocles. " For in truth I was born a boy and 

 a maiden, and a plant and a bird, and a fish whose 

 course lies in the sea." Our bodies may be buried or 

 burnt, but in either case the elements of which they are 

 composed will merely take other places in a never- 

 ending cycle, while the energy or soul of life will manifest 

 itself in other forms. 



The idea of the conservation of mass is easy to under- 

 stand, but that of the conservation of energy is less 

 obvious and is, perhaps, best explained by a concrete 

 illustration. When a certain amount of energy is caused 

 to actuate a machine, a certain amount of useful work 

 may be obtained from it, but the efficient output is 

 always less than the energy supplied, on account of loss 

 due to friction between various parts of the machine. 

 When the energy thus wasted is accounted for, the total 

 is the same as that of the original supply ; hence no 

 machine can be constructed to give out in the form of 

 available work as much energy as is put into it ; and, 

 therefore, perpetual motion is impossible. Expressed 

 in other words, we never get something for nothing in 

 Nature. Commission has to be paid whenever energy 

 is exchanged from one form into another ; and even 

 with the most efficient engine the charge for the trans- 

 formation is very high. 



The heat produced by the combustion of coal repre- 

 sents energy which is utilised to convert water into 



