OF ARTS AND SCIENCES. 229 



surface of the glass. The silvered mirror used was not perfect, and 

 a perfect silver surface would undoubtedly reflect more, — probably 

 as much as 91 or 92 per cent. Since relative results were desired, but 

 one reflecting angle was used in the above experiments. 



No. XX. — EFFECT OF DISTANCE ON APPRE- 

 CIATION OF COLOR. 



By W. H. Schwartz. 



Presented Dec. 10, 1879. 



Herbert Spencer, in his First Principles of Philosophy, adduces 

 the following as an instance of heterogeneity in the formation of the 

 Universe : — 



" While the yellow stars are found in all parts of the heavens, the 

 red and blue stars are not so ; there are wide regions in which both 

 red and blue stars are rare ; there are regions in which the red are 

 comparatively abundant." 



Professor Trowbridge suggested to me that the relative distance of 

 the stars, and their relative size, might affect our perception of color, 

 and that a colored star might appear of a faint white or yellow tint on 

 a dark background, if it were distant, compared with a colored star 

 which was at a less distance : in other words, that Herbert Spencer's 

 instance could not be adduced as an evidence of heterogeneity. 



I therefore undertook the following investigation. 



The solar spectrum having been projected upon a white wall, I cov- 

 ered it by a white screen provided with vertical slits at various dis- 

 tances, and in this way compared my appreciation of the color seen 

 through these slits at various distances. I speedily found that the 

 following experiments with slips of colored paper represented the 

 results which I obtained with the normal colors of the spectrum, and 

 brought out the facts equally well. I therefore abandoned the spec- 

 trum, and confined myself to the colored papers. 



Red, Green, and Yellow. 



I first tried strips of red, green, and yellow on a white background. 

 The strips were about .0015 meter wide and .025 meter long. They 

 were parallel and about .01 meter apart. 



