STUDIES IN SPECIAL SENSE PHYSIOLOGY 



PART II 



SECTION I. HISTORICAL INTRODUCTION 



ANY one who examines the current text-books of physiology 

 will find that in discussing colour vision great prominence is 

 given to two theories, those of Helmholtz and Hering respectively. 

 As the reader will also find it admitted that neither theory resumes 

 in an altogether satisfactory manner the data of observation and 

 experiment, he may be tempted to ask why so much stress is put 

 upon them. An obvious explanation is the authority attaching 

 to any utterances of men who have notably advanced our know- 

 ledge in various fields. This cannot, however, be the sole reason ; 

 physiologists not less distinguished than Helmholtz and Hering have 

 before now promulgated theories which, being inconsistent with the 

 subsequent results of investigation, have perished. The vitality 

 of these particular theories of colour vision must therefore be 

 referred to some. principle other than that of mere authority. 



The object of this essay is to show that these admittedly in- 

 complete theories are important because each brings into prominence 

 one aspect of the problem ; the harmonising of these two aspects 

 must occupy those who come after us and examine the question 

 by the light of fuller knowledge than we possess. 



With this end in view, it will be necessary, before considering 

 the theories themselves and their relation to known facts, to 

 examine briefly some opinions as to the nature of visual processes 

 which were held long ago but have by no means lost all interest 

 for us. Of these speculations, the most important are due to the 

 Greek philosophers' and men of science. 1 



In attempting to estimate the scientific value of the Greek 

 theories of vision, it is necessary to bear in mind certain limitations 



1 A valuable account of Greek Sense Physiology and Psychology will be found 

 in "Greek Theories of Elementary Cognition from Alcmneon to Aristotle," by 

 Professor J. I. Beare (Clarendon Press, 1906, p. 354). 



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