30 CROONIAN LECTURES 



with them, and their reciprocal relations with 

 it and with each other. From the manner in 

 which the particular force called electricity 

 is seemingly transmitted through certain 

 bodies, such as metallic wires, the term cur- 

 rent is commonly used to denote its apparent 

 progress. 



"It is very difficult to present to the mind 

 any theory which will give a definite con- 

 ception of its modus agendi. The early 

 theories regard its phenomena as produced 

 either by a single fluid, idio-repulsive, but 

 attractive of all other matter ; or else as pro- 

 duced by two fluids, each idio-repulsive, but 

 attractive of the other. No substantive theory 

 has been proposed other than these two. But, 

 although this is the case, I think I shall not be 

 unsupported by many who have attentively 

 studied electrical phenomena, in viewing them 

 as resulting, not from the action of a fluid or 

 fluids, but as a molecular polarisation of or- 

 dinary matter, or as matter acting by attraction 

 and repulsion in a definite direction." 



Whenever we come to the third stage of ideas 

 regarding electricity and magnetism, like light 

 and heat, they will be regarded as peculiar 



