118 Prof. A. M. Mayer on the History of Young's 



and blue, in this the first publication of his hypothesis), " and 

 that each of the particles is capable of being put in motion, less 

 or more forcibly, by undulations differing less or more from a 

 perfect unison." This would suppose such a triple molecular 

 constitution of each nerve-fibril as to cause the three species of 

 its constituent molecules (or the atoms forming the molecules) 

 to be in tune with the three rates of vibration corresponding 

 respectively to the undulations of the aether causing red, yel- 

 low, and blue. He afterwards says, " and each sensitive fila- 

 ment of the nerve may consist of three portions, one for each 

 principal colour." We have here a conception of the mode of 

 action of an aetherial vibration on the retinal nerve-fibril which 

 has not been described by those who have given accounts of 

 Young's theory of colour-sensation. Before reading the cele- 

 brated Bakerian Lecture, the only knowledge I had directly 

 obtained of Young's theory was from the reading of the account 

 of it as published in vol. i. page 439 of his ' Lectures on Na- 

 tural Philosophy and the Mechanical Arts,' London, 1807. 

 This account, however, contains no mention of the physiolo- 

 gical part of his theory; and last May I published in the Phi- 

 losophical Magazine my paper No. 6 of " Researches in Acous- 

 tics," in which (p. 363) I expressed similar views to those just 

 quoted from Young, as follows : — 



" For, has modern histology given us any facts concerning 

 the structure of the human retina which point to the establish- 

 ment of Young's hypothesis of three distinct sets of retinal 

 nerve terminations ? The more we study the minute structure 

 of the retinal rods and cones, the further appears to remove an 

 understanding of the mode of operation of the sensory appa- 

 ratus of the eye. May not research in this direction be guided 

 by the hypothesis that the molecular constitution of the retinal 

 rods and cones is such that their molecules are severally tuned 

 to the vibrations corresponding to the colours red, green, and 

 violet? This would lead us to look for effects of actinism on 

 the retina as showing the link existing between the transmit- 

 ting and sensory functions of the eye. Do not the facts of the 

 known persistence of chemical action, after it has been once 

 initiated, and the time which would be required for the retinal 

 molecules to recombine or rearrange themselves after the aethe- 

 rial vibrations had ceased, comport with the known durations 

 of the residual visual sensations, and with the main facts of 

 physiological optics, better than the hypothesis that masses of 

 the retinal elements are set in vibration rather than their mo- 

 lecules?" 



It requires no argument, it is evident, that the statements 

 made by Young in the foregoing paper, concerning his colour 



