470 DR WILLIAM POLE ON THE PRESENT STATE OF 



Professor Rutherford, 1892. 



I need only allude to the address by Professor Eutherford ; — it will be fresh in the 

 recollection of all interested in this subject, and it is to be hoped he will supplement it 

 by some further communications. 



Professor Von Helmholtz, 1892. 



I have reserved to the last a most important part of my work, i.e., a notice of the 

 latest published views of the philosopher who must, I suppose, be considered the highest 

 living authority on this matter. 



The part of Helmholtz's great work, Handbuch der Physiologischen Ojrtik, containing 

 the subject of colour- vision, originally appeared in 1860, but a new and revised edition is 

 now publishing ; and it is a matter of great interest to see what alteration the march of 

 scientific investigation has led him to make in his views. I have endeavoured to institute, 

 in the Phil. Mag. of Jan. 1893, a careful comparison between the two editions, and, as 

 the alterations are material, I will give a summary here of how they affect our know- 

 ledge. 



I do not find that Helmholtz, even in his first edition, has given any countenance to 

 the vexatious and pertinacious opposition offered by his followers to the assertions of the 

 colour-blind, that their warm colour appeared to correspond with the normal yellow, for 

 in the very outset of his descriptions he mentions this fact in several ways, and accom- 

 panies it with a demonstration that " for an eye which confuses red with green, all hues 

 seen may be compounded of yellow and blue." I believe his objection was strictly of 

 the same nature as that of Maxwell, described in page 449. At the same time, as he 

 undoubtedly promulgated the popular idea that dichromic vision was, according to Young's 

 theory, due to the inaction of one of the three colour-perceiving elements, and the 

 activity of the two others ; and as this is the point which has been so much contested, it 

 becomes most important to inquire what attitude the great philosopher has taken in regard 

 to it in his latest publication. 



The first thing we notice is a short but very significant new passage in which we find 

 he speaks of the above-mentioned theory as an "old attempt to explain colour-blindness," 

 contrasting it with a more recent one ; he speaks of the explanation of colour-blindness 

 as an " enigma," and adds that it has lately become probable that its solution is to be 

 sought in another direction. From this we are bound to infer that he no longer insists 

 on his former mode of explanation ; and this inference is confirmed by many subsequent 

 passages in the same strain. 



The new method of explanation, we may say at once, is pointed out to be that 

 originated by himself, and afterwards expounded by Leber, Fick, and Konig, as de- 

 scribed ante, pages 465, 466, and 469, namely, the combination of the two fundamental 

 sensations, red and green, to form yellow. 



