276 GREAT MEN OF SCIENCE 



bodies which attract one another, such as the raising of a 

 weight, signifies a storage of work, and that in the chemical 

 separation of bodies the same thing holds; 'the chemically- 

 separated existence' for example of carbon and oxygen or 

 chlorine and hydrogen is also 'a force' ('form of energy' as 

 we prefer to say to-day), and when this form of energy disap- 

 pears, namely when the separation ceases, heat is again pro- 

 duced, as in a coal-fire. Thus Mayer for the first time 

 throws entirely new light on the old and well-known pro- 

 duction of heat in chemical processes, which had first been 

 regarded as the setting free of a chemical component (heat- 

 stuff), and then - when this explanation was shown to be 

 incorrect - remained devoid of all explanation. 



This new point of view put the whole matter and many 

 others in a new and important connection. It thus also be- 

 comes clear that the development of heat by electric cur- 

 rents takes place at the cost of the chemical energy used up 

 in the voltaic cells. Also, the work stored in electrically 

 charged bodies, which is shown by phenomena of attrac- 

 tion and repulsion, in the effects of the spark and other heat 

 phenomena on discharge, can only be produced by expendi- 

 ture of work - as Robert Mayer made clear for the first time - 

 for in every such case it is a matter of separating the two op- 

 posite kinds of electricity, and since these attract one another 

 this separation can only be effected by expenditure of work, 

 whether this takes place in the electrophorus by influence, or 

 in the frictional electric machine, or in Volta's manner by 

 contact between conductors of the first class. 



Mayer thus arrives at a statement of the five different forms 

 of energy, which we also enumerate to-day: i. Potential 

 Energy (energy ot position); 2. Kinetic Energy (energy of 

 motion); 3. Heaf 4. Electro-magnetic Energy; 5. Chemical 

 Energy.! 'jj^ ^11 physical and chemical processes the given 



1 Mayer's terms are only slightly different (see the previous footnote), 

 and he explained quite unambiguously the terms which he uses. 



