SENSATION AND THE SENSIFEROUS ORGANS 293 



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 

 immediate instrument by which ideas are presented to the 

 mind ; or, in other words, whatever changes are made in this 

 substance, corresponding changes are made in our ideas ; and 

 vice versa. " 2 



Hartley, like Haller, had no conception of the 

 nature and functions of the grey matter of the 

 brain. But, if for " white medullary substance," 

 in the latter paragraph, we substitute "grey 

 cellular substance," Hartley's propositions embody 



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



2 Ibid. p. 8. The speciilations of Bonnet are remarkably 

 similar to those of Hartley ; and they appear to have originated 

 independently, though the Essai de Psychologic (1754) is of five 

 years' later date than the Observations on Man (1749). 



