A Syntonic Hypothesis of Colour Vision. 339 



for the former as it may do for the latter. It may be, how- 

 ever, that syntonic responses initiate changes of a physio- 

 logical or chemical character which in turn affect the 

 nerves. 



Experiments are here described with a set of three 

 vibrating responders in the shape of pendulums whose 

 relative vibrational frequencies correspond to red, green, and 

 violet. This crude experimental representation is allowable 

 and may be highly useful because the mathematical theory 

 of forced vibrations is almost independent of the exact form 

 of the vibrators themselves. 



These three pendulum responders are found to be sufficient 

 to imitate most of the fundamental facts of colour vision. 

 Others, such as persistence of vision and irradiation, are 

 then supposed to be due to the comparative slowness of the 

 physiological changes and their spreading round the spot on 

 the retina where they originated. 



2. Some Fundamental Facts of Vision. 



For the present purpose we may summarize the most 

 important facts of colour vision as follows : — 



(a) The range of visual sensations corresponds to rather 

 less than an octave, or the wave-length varies from about 

 0*76 fju to 0'4yu,, the frequencies being nearly (4 to 7'6) X 10 14 

 per second. 



(6) The possibility of making white and matching any 

 colour by the true addition of red, green, and violet. 



(c) Tlie true addition of red and green give the appearance 

 of yellow. 



(d) The true addition of blue and yellow do not give 

 green but white (or pink). 



(<?) The true addition of red and violet give a purple 

 which is not found in the spectrum. 



(/) About thirty colours can be discriminated in the 

 spectrum, each one appearing to be a monochromatic patch. 



(g) A period of about one tenth of a second is needed for 

 fully acquiring or losing visual sensations. 



(h) The occurrence of irradiation or the spreading of very 

 bright images on the retina. 



All the above are for persons with both sight and colour 

 vision normal. For colour-blind persons one (or more) colour 

 sensation seems to be absent. 



It is well here to contrast the eye and the ear. 



