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 
; ss state of consciousness we call a “dull red 
a ht” —a little greater intensity to another which 
| we e call a “bright red light;” increase the mten- 
4 sity, and the light besomes white ; and, finally, it 
- dazzles, and a new state of consciousness arises, 
| een 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 
al es of conciousness will be the same, however 
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 
tl - 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 siiniles 
M 2 
