172 THE THEORY OF SENSATION'. 



inter se continentur." And if this be the case with different depart- 

 ments of secular knowledge, so is it between the entire encyclopedia 

 of such knowledge on the one hand, and the truths of revelation on 

 the other. Both proceeding from one and the same Author there 

 never can be variance between them, while the more diligently we 

 investigate the wonders of the natural world, whether of matter or of 

 mind, the more prepared shall we be to adore the perfections of the 

 infinite Creator, and the more capable of appreciating the unspeak- 

 able value of that boon, which he has given us in His revealed word, 

 to serve as a friendly beacon to guide us over those troubled waters 

 which unaided reason cannot safely navigate ; and through that 

 dark, eternity-concealing gloom which the eye of human science, 

 however keen its glance, is unable to pierce. 



Hoping, Mr. President, that I may be pardoned for these pre- 

 liminaiy observations, I will proceed, without further preface, to 

 bring before you that interesting branch of mental science — 

 Sensation. 



In treating this evening on "The Theory of Sensation," it 

 is my wish to present to you the subject at large, rather than 

 any particular view of it ; to shew rather how little we know than 

 how much, and, by referring, for the purj^ose of refutation, to the 

 various theories which philosophers have propounded in different 

 ages, to support, in conclusion, that theory which, because it has in it 

 the least of what is too often mistaken for theory, seems to myself 

 to be the most philosophical, and the most true. 



Sensatio7i I define to be, a general expression for those states of 

 mind which immediately follow the effects produced by external 

 objects on the organs of sense. 



The explanation of the mode in which external objects produce 

 these mental states, is what I understand by " The Theory of 

 Sensation." 



Anciently one term alone was applied to the apprehension by the 

 mind of what is extraneous to itself. In later days the mental process 

 has been further analized, and the term sensation restricted to what 

 Abercrombie and others term " the corporeal part of the process," 

 while perception is the word employed to denote the reference which 

 the mind makes to external objects as the cause of its sensations. 

 With perception, in this sense, I have nothing to do this evening. I 

 exclude altogether from my inquiry the manner in which the mind 

 obtains its knowledge of the external world, and its true estimate of 

 the objects of sensation. I have merely to treat of the effect pro- 

 duced on the mind by those objects, not the reference of the mind 

 to them. Still I cannot admit that I have to do only with " the 

 corporeal part of the process," since the corporeal part is strictly 

 nothing more than the effect produced oir the bodily organs. There 

 may be this bodily change unattended with any mental conscious- 

 ness. The nerves may be affected, and not the sentient mind. 

 When life is extinct, the landscape may be depicted in miniature 

 beauty and exactness on the retina, yet there will be no vision, no 

 mental apprehension of the loveliness. It is the mental conscious- 



