18 CORRELATION OF PHYSICAL FORCES. 



Habit and the identification of thoughts with phenomena 

 so compel the use of recognised terms, that we cannot avoid 

 using the word cause even in the sense to which objection is 

 taken ; and if we struck it out of our vocabulary, our lan- 

 guage, in speaking of successive changes, would be unintelli- 

 gible to the present generation. The common error, if I am 

 right in supposing it to be such, consists in the abstraction of 

 cause, and in supposing in each case a general secondary 

 cause a something which is not the first cause, but which, if 

 we examine it carefully, must have all the attributes of a first 

 cause, and an existence independent of, and dominant over, 

 matter. 



The relations of electricity and magnetism afford us a 

 very instructive example of the belief in secondary causa- 

 tion. Subsequent to the discovery by Oersted of electro-mag- 

 netism, and prior to that by Faraday of magneto-electricity, 

 electricity and magnetism were believed by the highest author- 

 ities to stand in the relation of cause and effect i. e. elec- 

 tricity was regarded as the cause, and magnetism as the effect ; 

 and where magnets existed without any apparent electrical 

 currents to cause their magnetism, hypothetical currents 

 were supposed, for the purpose of carrying out the caus- 

 ative view ; but magnetism may now be said with equal 

 truth to be the cause of electricity, and electrical currents 

 may be referred to hypothetical magnetic lines : if therefore 

 electricity cause magnetism, and magnetism cause electricity, 

 why then electricity causes electricity, which becomes, so to 

 speak, a reductio ad absurdum of the doctrine. 



To take another instance, which may render these posi- 

 tions more intelligible. By heating bars of bismuth and anti- 

 mony in contact, a current of electricity is produced ; and if 

 their extremities be united by a fine wire, the wire is heated. 

 Now here the electricity in the metals is said to be caused 

 by heat, and the heat in the wire to be caused by electricity, 

 and in a concrete sense this is true ; but can we thence say 



