458 



The Relation of Liglit Perception to Colour Perception. 

 By F. W. Edridge-Grben-, M.D., F.E.C.S., Beit Medical Research Fellow. 



(Communicated by Prof. E. H. Starling, F.R.S. Received June 3, — Read 



June 30, 1910.) 



(From the Institute of Physiology, University College.) 



Since the majority of the theories of colour perception wliich have been 

 propounded have been really theories of light perception, the two subjects, 

 namely, colour and light perception, though really quite distinct, have 

 become so intei'woven in the discussion of the question that many seem 

 quite incapable of distinguishing tlie two. Yet it may be easily shown that 

 light perception and colour perception are quite distinct. In fact, we can 

 divide cases of colour blindness into two classes, according as the defect is 

 («) one of light perception, or (&) one of colour perception or differentiation 

 without any defect in light perception. Of course, both defects may be 

 present in the same individual. 



The investigation of these two classes of defective vision is much 

 facilitated by the Use of a spectrometer which I have devised for the purpose, 

 and which is so arranged as to make it possible to expose to view in the 

 eye-piece the portion of a spectrum between any two desired wave-lengths. 

 It consists of the usual parts of a prism spectroscope, i.e. a colHmator 

 with adjustable slit, prism, and telescope with eye-piece of the following 

 dimensions : — 



Focal length of collimator and telescope object glasses = 7J inches (180 mm.). 



Clear aperture of collimator and telescope object glasses = J inch (22 mm.). 



Slit, 7 mm. effective length of jaw, with wedge for reducing the effective length of 



the slit, protective cap, compai'ison i)rism, and screw adjustment for the slit 



width, witli divided head. 



The prism is of flint glass, 1"65 refractive inde.x for I). Eye-piece, Ranisden 

 form, focussing on to tlie sliutters described below. 



In the focal plane of tlie telescope are two adjustable shutters with 

 vertical edges, the shutters being carried by levers which rotate about centres 

 near the object glass of the telescope. The shutters can be moved into the 

 field irom right and left respectively, each by its own micrometer screw, 

 and to each screw is attached a drum, the one being on the right and tlie 

 other on the left of the telescope. On each of these drums is cut a helical 

 slot in which runs an iii(l(!x, and tlic drum is engraved in such a iiiamier 

 that the reading of the inde.\ gives directly in wave-lengths the positimi in 

 the spectrum of the corresponding shutter. 



