92 Traces of Unity in the Various 



others together. Thus, " when a substance, such as sul- 

 phuret of antimony, is electrified, at the instant of elec- 

 trization it becomes magnetic in directions at right angles 

 to the lines of electric force ; at the same time it becomes 

 heated to an extent greater or less according to the in- 

 tensity of the electric force. If this intensity be exalted 

 to a certain point the sulphuret becomes luminous, or 

 light is produced : it expands, consequently motion is 

 produced ; and it is decomposed, therefore chemical 

 action is produced." Each force in relation to every other 

 force may be looked upon as cause and effect ; and it 

 would seem to be an irresistible inference from ob- 

 served phenomena that any one force cannot originate 

 except by devolution from some pre-existing force or 

 forces. 



Simple motion is resolved into heat, when an anvil 

 is beaten by a hammer, when a wheel grates upon 

 its axle, and in a thousand other ways. Where the 

 moving and resisting bodies are homogeneous, as when 

 iron encounters iron, the resolution of motion is chiefly 

 into heat, though light also often puts in a claim 

 to be noticed, as when fire is the result of percussion 

 or friction. Where the moving and resisting bodies are 

 heterogeneous, as in the case of the ordinary electrical 

 machine, where glass encounters the rubber coated with 

 amalgam, motion is resolved chiefly into electricity. The 

 resolution of motion into other modes of force is also 

 beautifully illustrated by an original experiment ex- 

 hibited by the author of the ' Correlation of the Physical 

 Forces ' in the lectures in which he first made known his 

 views, and of which the following account is to be found, 

 not in the work under consideration, but in the inaugural 

 address on " Continuity," delivered by him, as president, 

 at the meeting of the British Association held at Not- 



