94? DISCOURSE ON THE STUDY 



serving those with which it is habitually associated, 

 that may help us at length to its analysis. It is 

 thus that sciences increase, and acquire a mu- 

 tual .relation and dependency. It is thus, too, 

 that we are at length enabled to trace parallels 

 and analogies between great branches of science 

 themselves, which at length terminate in a percep- 

 tion of their dependence on some common phe- 

 nomenon of a more general and elementary nature 

 than thac which form the subject of either se- 

 parately. It was thus, for example, that, previous 

 to Oersted's great discovery of electro-magnetism, 

 a general resemblance between the two sciences of 

 electricity and magnetism was recognised, and 

 many of the chief phenomena in each were ascer- 

 tained to have their parallels, mutatis mutandis, in 

 the other. It was thus, too, that an analogy sub- 

 sisting between sound and light has been gradually 

 traced into a closeness of agreement, which can 

 hardly leave any reasonable doubt of their ulti- 

 mate coincidence in one common phenomenon, the 

 vibratory motion of an elastic medium. If it be 

 allowed to pursue our illustration from chemistry, 

 and to ground its application not on what has been, 

 but on what may one day be, done, it is thus that 

 the general family resemblance between certain 

 groups of bodies, now regarded as elementary, 

 (as nickel and cobalt, for instance, chlorine, iode, 

 and brome,) will, perhaps, lead us hereafter to per- 

 ceive relations between them of a more intimate 

 kind than we can at present trace. 



(86.) On those phenomena which are most fre- 

 quently encountered in an analysis of nature and 



