424 STUDIES IN SPECIAL SENSE PHYSIOLOGY 



adequate to the task of describing all the experimental facts, we 

 encounter difficulties not less formidable than those we found to 

 be associated with the Young-Helmholtz theory. 



In attempting to meet their respective difficulties, the two 

 theories become unsatisfactory in different ways. The stimulus 

 hypothesis becomes too general, the sensational hypothesis too 

 detailed. Examples have been described in the former's treat- 

 ment of dichromatic vision and the latter's account of after- 

 images. 



Perhaps the most tempting inference is that these theories are 

 in a sense complementary that they both contain some measure 

 of truth, surveying the vast complex of phenomena from very 

 different points of view. Neither theory is wholly true nor yet 

 wholly false ; nor does adhesion to the one imply total rejection 

 of its ostensible rival. 



I am only too conscious that, like Canning's clerical friend, in 

 being brief I have by no means escaped being tedious. My only 

 excuse, and that but a poor one, is that if we are ever able to pro- 

 pound a complete theory of the visual processes, this comprehensive 

 formula will embrace both those I have described, and until that 

 time comes a critical examination and comparison of both lines 

 of thought will always be indispensable to those who wish to gain 

 a real knowledge of visual physiology. In conclusion, the reader 

 is most earnestly recommended to consult the original memoirs of 

 Hering and the treatise of Helmholtz dealing with this subject. 

 He will not, indeed, find them light reading no really scientific 

 books are ; but he will be repaid by a grasp of the matter in hand 

 such as can never be derived from text-books, however lucid, or 

 summaries, however long. 



BIBLIOGRAPHY 



1 Beare, op. cit., p. 18. 



2 Aristotle, De Sensu et Scnsilibus, Taylor's Trans., vol. iii., p. 133. 



3 Beare, op. cit, pp. 36-37. 



4 Plato, Timoeiis, Jowett's Translation, vol. ii., pp. 538-9. 



5 Helmholtz, Handb. d. Phys. Optik., 2nd edit., p. 248. 



Plato, Thesetetus, Jowett's Trans., vol. iii., pp. 375, 378. 



7 Beare, op. cit., p. 64. 



8 Beare, op. cit., p. 69. 



9 Helmholtz, Handb. d. Phys. Opt., pp. 328-330. 



