184 THK THKOHV Of SENSATIOX. 



of every intervening link between the phenomena still leaves undis- 

 covered the connexion of those links with each other. As Dr. Thomas 

 Brown has profoundly reasoned and beautifully exemplified, invariable 

 antecedence is all we know of cause, invariable sequence all we know 

 of effect. 



The greatest discovery of modem times, nay, in the entire history 

 of science, namely, gravitation, is nothing more than this. If I am 

 told that an apple falls to the ground and that the earth is retained 

 in its orbit, by gravitation, this is no explanation of the facts, it is 

 only a vast generalization of them ; and though we were to adopt 

 the gi*eat discoverer's theory of an invisible ether which was the 

 agent in attraction, this would be nothing but another link in the 

 succession. Why the ether possessed the tendency to attract, and how 

 it exerted it, would still be unexplained. 



Leaving now the theories of other days, let us enquire " what is 

 the explanation afforded of Sensation at present ?" The preceding 

 enquiry, by teaching us our ignorance and the error of supposing 

 our knowledge is enlarged by hypotheses, will be seen not to be 

 irrelevant to this part of the subject, nay, will supersede the neces- 

 sity of any enlargement upon it. For men have at length, though 

 it has been by a laborious process, been taught the true method of 

 philosophising, and have learnt, if nothing else, at least their ignor- 

 ance. The explanation which Socrates gave of the response of the 

 Oracle * totycx yow rovrov ye a-fLix-pu Tivi ocvru rovru j-o^unfos sivaci ortac 

 fAvi oi^a. ov^e otofjixt et^svai', is applicable to this as well as every other 

 branch of science, for they are the wisest who are the most willing 

 to confess their ignorance. What, then, is the theory of Sensation 

 generally adopted now ? That external objects, by the medium of 

 light and air, or by apparent contact, produce some change in the 

 orijans of sense, the nature of which change is unknown — that this 

 impression is conveyed along the nerves in some manner unknown to 

 the brain, v.hich is affected thereby in some way unknown— and 

 that the mental state called sensation immediately results in some 

 method also unknown. 



Now, gi'eat as is the wisdom of ignorance contained in this the(uur, 

 I am disposed to think that even it pretends to too much knowledge. 

 That there is the external object we have intuitive belief; that it 

 affects the organ either by light as in vision, or vibrations in the air 

 as in hearing, or by minute particles emitted as in smell, or by 

 apparent contact as in touch and taste, we have experimental evidence, 

 that there is the resulting sensation we have the testimony of con- 

 sciousness ; so that the first, second, and fourth parts of the theory 

 are well established, but what sufficient evidence have we of the third? 

 Or to revert to our former threefold classification, we have the first 

 stage of the journey accounted for, namely, the impression on the 

 sensitive organ; and the third stage, namely, the effect produced on 

 the mind; but what proof have we of the second, namely, the transfer 

 of the impression from the organ of sense to the brain as the seat 

 of the soul ? 



I anticipate the reply of many present, a reply, in substance. 



