PHILOSOPHICAL SOCIETY OF WASHINGTON. 55 



and there transformed into a distinct sensation. The same would 

 hold good probably for the orange, yellow, green, blue and violet. 

 We have an analogy for such reaction in the molecular change pro- 

 duced by light in the metal selenium when in a crystallized state, 

 and in some other substances. The photophone depends for its 

 existence upon this delicate reaction of the molecular structure of 

 selenium to the influence of light. Which are the primary and 

 which the secondary colors — that is those arising from mixed sen- 

 sations — would have to be determined by experiment. 



The speaker would divide color blindness into two classes, peri- 

 pheral and central. In the former the retina and optic nerve would be 

 the agents affected, in the latter the cerebral centre of vision. The 

 latter he considered to be the most common form of congenital color 

 blindness, and it was due in his opinion to the fact that this centre 

 had not yet developed the power of properly differentiating the 

 closely allied impressions sent to it. In such cases, the spectrum 

 was not shortened, but was seen dichromic, the line of demarca- 

 tion being usually at the blue. 



As regards the retinal form one broad general principle might be 

 laid down, that where there was a lacking color the molecular 

 changes in the retina were such as to incapacitate it from respond- 

 ing promptly to the wave lengths which physically represent that 

 color. 



Believing that education had much to do with the development of 

 the color-sense, the speaker had devised a plan for the " systematic 

 education of the color-sense in children," which, if followed out 

 closely, would, he believed, in the course of generations, make color- 

 blindness as rare in the male sex as it now is among females. This 

 plan is published in full in the Archives of Ophthalmology. (G. 

 P. Putnam's Sons, New York, October, 1879.) 



The next communication was by Mr. E. M. Gallaudet, en- 

 titled— 



THE INTERNATIONAL CONVENTION OF THE TEACHERS OF THE 

 DEAF AND DUMB, AT MILAN. 



Mr. Gallaudet recited first certain resolutions adopted at that 

 convention, which were as follows : 



" The convention, considering the incontestable superiority of 

 speech over signs, 1st, for restoring deaf-mutes to social life, 2d, 

 for giving them greater facility of language, declares that the 



