THE FORMS OF ENERGY. 115 



stances into their constituent elements, the heat disappearing with no 

 other result than the separation of the elements ; while, on the other 

 hand, there are numerous familiar examples of the appearance of heat 

 on the union of elements or the chemical combination of previously 

 separated substances. In the voltaic cell, chemical combination occurs 

 when the cell is in action, while in and round the circuit heat is 

 produced, or magnetic actions occur, or light issues from sparks, and 

 these energies we suppose to have come from the constituents in the cell 

 through the intermediate forms of electric and magnetic energies. Con- 

 versely, the electric current decomposes substances the electric and 

 magnetic energies being transformed now into the energy of chemical 

 separation. 



The following list includes all the distinct forms of energy which 

 have yet been recognised : 



1. Kinetic Energy. 



2. Potential 



3. Heat 



4. Strain ,, 



(1 and 4 are also combined in Sound.) 



5. Light and Radiant Energy. 



6. Electric 



7. Magnetic 



8. Chemical 



We have already given many examples in which the disappearance 

 of one of these forms is accompanied by the appearance of one or more 

 of the other forms, and our observations and experiments justify us in 

 regarding such accompaniment as the universal rule. There is no example 

 in which one kind of energy is absolutely annihilated without the appear- 

 ance of another, nor in which one kind of energy appears de novo without 

 the loss of another. Indeed, so far convinced are we of this, that an 

 apparent exception would lead us to suspect, not the truth of this state- 

 ment, but the completeness of our list of energies. We should at once 

 look out for a hitherto unrecognised form which appeared or disappeared, 

 and endeavour to obtain some independent evidence of its existence and 

 only after most careful research and failure to find such a form could we 

 suppose that energy was annihilated or came into existence de novo. It is, 

 of course, quite possible, that there are forms of energy yet unrecognised. 

 If we happened to observe the disappearance of energy at one time or 

 place, and the appearance in connection with it of energy at another time 

 or place, and yet could not suppose the existence of any yet known form 

 as connecting link between the two, we should be driven to suppose that 

 some form existed, hitherto unknown, so that the disappearing energy 

 took this form and that on its reappearance it emerged from it, and we 

 should at once look out for the conditions implying the new form. If, for 

 example, the cases of so-called "telepathy" were placed beyond question, 

 we should probably have disappearance of energy from one individual 

 accompanied by its appearance in another at a distance, and it is quite 

 conceivable that we should have to suppose that the energy in the inter- 

 vening space was in a form not yet known. But up to the present the 

 evidence hardly warrants the assumption that our list is thus incomplete. 



