182 THK THEORY Or SKNSATIOV. 



by means of phantasms, is this : — first, that in some cases this is 

 inconceivable — in all, destitute of proof; secondly, that the axiom 

 on which the necessity for such a theory was based is questionable, 

 and if not questionable, illogically applied ; and thirdly, that all the 

 phenomena can be accounted for in another and a surer way. 



We observed that between the remote object of sensation and the 

 sensitive mind, philosophers seem to have reckoned three stages-*- 

 according to these we are now classifying their systems. We have 

 considered the reply of the ancients to the enquiry how can the 

 influence of the distant body be conveyed to the organ of sense ; let 

 us now consider the explanations which have been given of the 

 transfer of the impressions produced on the organ, to the seat of 

 the soul. 



In later times, the brain has been universally regarded as the 

 residence of the spirit, and various theories have been framed by 

 which to explain the conveyance thither of the intimations received 

 from foreign objects by the sensitive organs. Some, with Des 

 Cartes, have held that this is by means of the animal spirits, through 

 the tubes of the nerves ; others, with Hartley, that it is by vibra- 

 tions of the ether ; others, that it is by vibrations of the nei-ves, as 

 by musical chords. 



On these theories we obsen^e: — 



First. — That they are destitute of proof. Anatomists have, 

 hitherto, failed in discovering the Cartesian spirits; of the existence 

 of the ether and its motions, there is no evidence ; no vibrations of 

 the nerves have yet been observed, neither are they capable of this, 

 not being like musical chords in a state of tension. I observe. 



Secondly. — That supposing any of these various theories had been 

 true, the great mystery of the influence of matter on mind, for the 

 explanation of which they seem in great part to have been framed, 

 would still remain as inexplicable as ever. However skilfully the 

 diflferent links in the chain of material causation might be traced, 

 the connection with that which is immaterial is equally diflJicult 

 of explanation, at whatever part of the process it be attempted. 



To this, then, the third of the stages alluded to in our classifica- 

 tion of theories, we now direct your attention. How can the effect 

 produced by the nerves on the brain, the seat of the mind, be con- 

 veyed to the mind itself, so as to occasion sensation. 



We have seen that some philosophers deny any reciprocal agency 

 whatever. Des Cartes tells us that the bodily impression is only 

 the occasion on which God produces sensation in the mind ; and 

 Mallebranche says, that in sensation it is not outward objects, but 

 the ideas in the mind of the Deity by which we are affected. In 

 reply to this, I merely observe, first, that it is a mere hypothesis ; 

 and, secondly, that though the framers of the theories thought other- 

 wise, it adds neither to the glory of the great Creator and tFpholder 

 of the universe, nor to our dependence on Him, to suppose that His 

 operations are independent of one another, and in a sense disjointed, 

 rather than that they are the operations of general laws,by means of the 

 great machinery of instrumentality which he has ordained. Leibnitz, 



