NERVE FORCE A SPECIFIC FORCE. 167 



uble argument against Dr. Beale's hypothesis that 

 electricity is the nerve force, and exactly his theory of 

 muscular action adds insuperable force to the argu- 

 ment against the electric theory, for, although it might 

 not have mattered so much sending the force of a 

 mere stimulus, of which so small a quantity is needed, 

 through a bad conductor, how can we reconcile it with 

 the economy of nature, that a force which is to do the 

 whole work of the muscles should be sent through a 

 conductor which offers three million times the resist- 

 ance of mercury, and still more than that of silver or 

 copper ? "We are, I think, compelled to conclude that 

 the force must be a distinct force, not like heat, light, 

 or sound, but a current force, analogous to electricity, 

 galvanism, and magnetism, but distinct from these. 

 Perhaps this is what Dr. Beale means, and indeed 

 physicists generally describe these all as modifications 

 of electricity. Nevertheless, Professor Challis regards 

 these forces as essentially distinct. He says : 



" It is, I think, to be regretted that experimentalists use the 

 word ' electricity ' with so great a latitude as to its application. 

 The practice seems to have arisen from speculatively inferring 

 the identity of different physical forces from phenomena which 

 they have in common, and not giving sufficient consideration 

 to other circumstances by which they are distinguished." He 

 has " uniformly regarded ' electricity ' as an effect produced by 

 friction or other means exclusively at the surfaces of sub- 

 .stances," and he considers it quite distinct from galvanism. 

 He adds, " I have with satisfaction noticed that the Astronomer 

 Royal employs in the Greenwich observations the terms * gal- 

 vanism ' and 'galvanic signals ;' but electric telegraph is, I fear, 

 too established by common usage to be unsettled," p. 99. He 

 looks upon the galvanic current as very different from the 

 electric, but nearly resembling the magnetic, into which it is 



