108 PROCEEDINGS OF THE AMERICAN ACADEMY 



use to painters in mixing colors, as the effect of mixing any 

 two colors may be at once seen. Dove, of Berlin, has used 

 this instrument in showing that, when the eye has rested for a 

 certain time on a bright color and then is turned to a white 

 surface, the retina becomes partly insensible to the first color 

 and feels more strongly its complementary color. These ex- 

 periments were also shown. 



Dr. Hayes exhibited some of the juice of the India-rubber 

 tree, preserved from decomposition by a patent process. By 

 the addition of a weak alkali to the recent juice, a substance 

 prone to acetous fermentation is so changed that the forma- 

 tion of acid is prevented. This has led to many new applica- 

 tions of this useful substance. He exhibited specimens of 

 perfectly pure India-rubber obtained from this milky juice ; 

 the consistence of the latter is between that of milk and 

 cream ; it yields from 48 to 52 per cent, of solid India-rubber. 

 What he wished particularly to draw the attention of the 

 Academy to was the fact, that this substance, in its normal 

 state, is perfectly transparent ; it is curious that from this 

 entirely opaque fluid a transparent India-rubber should be ob- 

 tained by simple desiccation. He exhibited a glass vessel 

 coated inside and outside with this material, which did not in 

 the least diminish the transparency of the glass, and was rec- 

 ognizable only by the touch ; he had found that a considera- 

 ble number of coatings did not diminish the transparency. 



Dr. Kneeland read an abstract of the views of Messrs. Nott 

 and GHddon, as given in a work just published, entitled " Types 

 of Mankind," in which the strongest arguments are given in 

 favor of the theory of the original diversity of the human 

 races ; based in a great measure on the proofs derived from 

 the Egyptian monuments, that at least four human races have 

 remained distinct in and around the valley of the Nile from 

 ages anterior to 3,500 years B. C, and consequently long an- 

 terior to any alphabetic chronicles, sacred or profane ; the first 

 part of the book ending with the conclusion " that there ex- 

 ists a genus Homo embracing many primordial types or ' spe- 



