250 SENSATION AND THE SENSIFEKOUS ORGANS. [LECT, 



he had not apprehended the significance of the revo- 

 lution commenced, two hundred years before his 

 time, by Descartes, and effectively followed up by 

 Haller, Hartley, 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 " Ob- 

 servations 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." x 



"The white medullary substance of the brain is also the 



corpus quod sentimus : organi sensorii adfectio ab eo corpore : cerebri 

 adfectio a sensorii percussione nata : in anima nata mutatio : animse 

 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 consciousness 

 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. 



1 "Observations on Man," vol. i. p. 11. 



