SENSATION AND THE SENSIFEROUS ORGANS. 257 



he had not apprehended the significance of the revolu- 

 tion commenced, two hundred years before his time, by 

 Descartes, and effectively followed up by Haller, Hart- 

 ley, and Bonnet, in the middle of the last century. 



In truth, the theory of sensation, except in one point, 

 is, at the present moment, very much where Hartley, led 

 by a hint of Sir Isaac Newton's, left it, when, a hundred 

 and twenty years since, the " Observations on Man : his 

 Frame, his Duty, and his Expectations," was laid before 

 the world. The whole matter is put in a nutshell in the 

 following passages of this notable book. 



" External objects impressed upon the senses occasion, first on 

 the nerves on which they are impressed, and then on the brain, 

 vibrations of the small and, as we may say, infinitesimal medullary 

 particles. 



" These vibrations are motions backwards and forwards of the 

 small particles ; of the same kind with the oscillations of pendulums 

 and the tremblings of the particles of sounding bodies. They must 

 be conceived to be exceedingly short and small, so as not to have 

 the least efficacy to disturb or move the whole bodies of the nerves 

 or brain." * 



" The white medullary substance of the brain is also the imme- 

 diate instrument by which ideas are presented to the mind ; or, in 

 other words, whatever changes are made in this substance, corre- 

 sponding changes are made in our ideas ; and vice versa." f 



adf ectio ab co corpora : cerebri adf ectio a sensorii percussione nata : in 

 anima nata mutatio : aniraae denique conscientia et sensationis adperceptio." 

 Nevertheless, Sir William Hamilton gravely informs his hearers : " We 

 have no more right to deny that the mind feels at the finger points, as con- 

 sciousness assures us, than to assert that it thinks exclusively in the brain." 

 "Lecture on Metaphysics and Logic," ii. p. 128. "We have no reason 

 whatever to doubt the report of consciousness, that we actually perceive at 

 the external point of sensation, and that we perceive the material reality." 

 Ibid. p. 129. * " Observations on Man," vol. i. p. 11. 



f Ibid. p. 8. The speculations of Bonnet are remarkably similar to 



