16 CROONIAN LECTURES 



magnetism, that we have no proof of -the 

 materiality of electricity, or of the existence of 

 any current through the wire." 



With regard to the imponderable materiality 

 of the magnetic force. Descartes considered 

 magnetic curves to be the traces of currents of 

 setherial matter, which are thus rendered 

 sensible even to the eye. According to 

 .ZEpinus, the phenomena of the opposite poles 

 arose from an excess or defect of a magnetic 

 fluid. Coulomb assumed an austral and a 

 boreal fluid instead of a single fluid ; Whewell 

 says the hypothesis of magnetic fluids, as 

 physical realities, was never so widely or 

 strongly embraced as that of two electric fluids. 

 There was no spark, shock, discharge, or me- 

 chanical effects. He continues, "if we doubt 

 regarding electric fluids, we cannot help pro- 

 nouncing upon the magnetic fluids as having 

 still more insecure claims to a material exist- 

 ence. They must be regarded as different effects 

 of one common cause. No philosopher would 

 dream of assuming electric fluids and magnetic 

 fluids as two distinct material agents." 



Thus, then, in the second stage of ideas of 

 matter and force, force is made quite insepar- 



