194 COLOUR VISION 



The task which we have set before us is that of discovering in the 

 realm of vision " what psychical event a and what physical stimulus a 

 are universally connected in the order of nature, and of finding the 

 law by which a undergoes a definite change and becomes /3, when a by 

 a change equally definite (but definable only by a physical standard and 

 not a psychical one) becomes b (Lotze^)." In the accumulation of the 

 facts already set forth we may discern two distinct methods which I will 

 term the synthetic and the analytic. In every case there is a stimulus 

 which excites and a sensatipn of which the individual is conscious. 

 In most cases — one might say in all — both are complex. In the 

 investigation two methods may be adopted. In the first the stimulus 

 is reduced to its simplest form and the resulting sensation observed. 

 The sensation is evoked by the simplest possible physical stimuli : 

 hence the designation synthetic. In the second method the sensation 

 is reduced to its simplest form and the varieties of stimuli which 

 elicit this simple sensation are classified and analysed. This is the 

 analytic method. A priori one is inclined to attach more significance 

 to the results obtained by the synthetic method. It is the method 

 which prevails in the exact sciences, chemistry, physics, and so on. 

 Our sensations are notoriously liable to play us false. They are complex 

 and they are modified by all the other sensations to which the individual 

 is subject at the moment of observation. It is impossible to nullify 

 all the conflicting sensations and it is easy to overlook those potent to 

 mislead. On the other hand the problem itself deals with the sensation 

 and its modifications, and it may therefore be reasonably urged that 

 the analytic method of attack is of the essence of the problem. In 

 the exact sciences the sensations involved are generally simple and 

 well-defined and their modifications either complicate the observations 

 little, or are so disturbing as to indicate their own corrective. They 

 are one cause of " errors of observation," and the manner in which 

 these are minimised in the exact sciences is familiar to all. 



The two methods are not antagonistic but complementary, and as 

 such should lead to identical results. That they do not is the fault of 

 ignorance and is not due to any innate defects. If we had certain 

 knowledge of all the effective factors in the physical stimuli and of all 

 the efiective factors in the resultant sensations and of all their quantita- 

 tive and qualitative relations, we should arrive at consistent results. 

 But that is a truism. It is the role of physiology to deal with com- 

 plex relations of this nature, and especially the role of physiological 



^ Metaphysik; Bosanquet's translation, 295, 1894. 



