v MR. DARWIN'S CRITICS 163 



being expressed by one another, just as heat and 

 mechanical action are capable of being expressed 

 in terms of one another. Whether we shall ever 

 be able to express consciousness in foot-pounds, or 

 not, is more than I will venture to say ; but that 

 there is evidence of the existence of some corre- 

 lation between mechanical motion and conscious- 

 ness, is as plain as anything can be. Suppose the 

 poles of an electric battery to be connected by 

 a platinum wire. A certain intensity of the 

 current gives rise in the mind of a bystander to 

 that state of consciousness we call a " dull red 

 light " a little greater intensity to another which 

 we call a " bright red light ; " increase the inten- 

 sity, and the light becomes white ; and, finally, it 

 dazzles, and a new state of consciousness arises, 

 which we term pain. Given the same wire and 

 the same nervous apparatus, and the amount of 

 electric force required to give rise to these several 

 states of conciousness will be the same, however 

 often the experiment is repeated. And as the 

 electric force, the light waves, and the nerve- 

 vibrations caused by the impact of the light- waves 

 on the retina, are all expressions of the molecular 

 changes which are taking place in the elements of 

 the battery ; so consciousness is, in the same 

 sense, an expression of the molecular changes 

 which take place in that nervous matter, which is 

 the organ of consciousness. 



And, since this, and any number of similar 



M 2 



