History of Young's Discovery of his Theory of Colours. Ill 



stream-line. This, of course, is also true when the molecular 

 rotation is not zero, but any constant. 



When the motion is not confined to one plane, the energy 

 of the fluid will be uniformly distributed in any case in which 

 the molecular rotation is zero, or more generally when the axis 

 of rotation of a fluid element is likewise the direction of its 

 motion of translation ; but the consideration of this kind of mo- 

 tion is postponed for the present. 



XV. The History of Young's Discovery of his Theory of 

 Colours. By Alfred M. Mayer. 



To the Editors of the Philosophical Magazine and Journal. 



Stevens Institute of Technology, Hoboken, 

 GENTLEMEN, New Jersey, December 13, 1875. 



I HAVE the honour to send you for publication in your 

 Journal the accompanying paper, entitled " The History 

 of Young's Discovery of his Theory of Colours." Disjointed 

 extracts from this paper have appeared in English journals; 

 and I am therefore desirous that the entire paper should appear 

 in your Journal, if you should deem it worthy of that di- 

 stinction. 



I remain, Gentlemen , 



Yery respectfully yours, 



Alfred M. Mayer, 



The object of this communication is twofold : I desire first 

 to give complete abstracts from the writings of Newton, 

 Young, and Wollaston, in order to put the student of science 

 in possession of all of the early literature relating to Young's 

 theory of colours : in the second place, I propose to trace the 

 curious history of the steps by which Young was led to the 

 final adoption of what is now known as Young's theory of 

 colour-sensation. In accomplishing the first of these objects, 

 I shall at the same time attempt to show, 1st, that Young first 

 formed an hypothesis similar to that known as Brewster's 

 (that is, he selected red, yellow, and blue as the three simple 

 colour-sensations); 2nd, that he subsequently modified his 

 hypothesis and adopted red, green, and violet as the three ele- 

 mentary colour-sensations, showing that up to the date of this 

 change of opinion all of his ideas on the subject were hypo- 

 thetical, and not based on any observations or experiments of 

 his own or of others ; 3rd, that this change of opinion as to 

 the three elementary colours was made on the basis of a mis- 

 conception by Wollaston of the nature of his celebrated obser- 



