X.] SENSATION AND THE SENSIFEROUS ORGANS. 249 



sensory operations have been, from time immemorial, 

 the battle-ground of philosophers. 



I have more than once taken occasion to point 

 out that we are indebted to Descartes, who happened 

 to be a physiologist as well as a philosopher, for the 

 first distinct enunciation of the essential elements of 

 the true theory of sensation. In later times, it is not 

 to the works of the philosophers, if Hartley and James 

 Mill are excepted, but to those of the physiologists, 

 that we must turn for an adequate account of the 

 sensory process. Haller's luminous, though summary, 

 account of sensation in his admirable " Primse Lineae," 

 the first edition of which was printed in 1747, offers 

 a striking contrast to the prolixity and confusion of 

 thought which prevade Keid's " Inquiry," of seventeen 

 years' later date. 1 Even Sir William Hamilton, 

 learned historian and acute critic as he was, not only 

 failed to apprehend the philosophical bearing of long- 

 established physiological truths ; but, when he affirmed 

 that there is no reason to deny that the mind feels 

 at the finger points, and none to assert that the 

 brain is the sole organ of thought, 2 he showed that 



1 In justice to Reid, however, it should be stated that the chapters 

 on sensation in the " Essays on the Intellectual Powers " (1785) exhibit 

 a great improvement. He is, in fact, in advance of his commentator, as 

 the note to Essay II. chap. ii. p. 248 of Hamilton's edition shows. 



2 Haller, amplifying Descartes, writes in the " Primaa Lineae," 

 CCCLXVI. "Non est adeo obscurum sensum omnem oriri a*b objecti 

 sensibilis impressione in nervum quemcumque corporis humani, et 

 eamdem per eum nervum ad cerebrum pervenientem tune demum re- 

 presentari animse, quando cerebrum adtigit. Ut etiam hoc falsum sit 

 animam inproximo per sensoria nervorumque ramos sentire." .'.,. 

 DLVII. " Dum ergo sentimus quinque diversissima entia conjunguntur : 



