A. W. Whitney — Refraction of Light upon the Snow. 389 



Art. XLIY. — Refraction of Light upon the Snow •* by 

 Albert W. Whitney. 



Under certain conditions involving the character of the 

 snow and the altitude and brilliancy of the sun, the glitter of 

 the snow is not uniform. Make these conditions, then, a cold, 

 clear, winter afternoon, about half an hour before sunset, and a 

 rather fresh field of snow, and the following description becomes 

 general. 



Two roughly Y-shaped paths, of especial, not exclusive, bril- 

 liancy, open away from the observer and towards the sun ; the 

 apex of one is perhaps six feet away, its angle 90° ; the apex 

 of the other is perhaps 15 feet away, its angle 60°. 



The following facts are to be noted : 



First, the light is not diffused ; it is made up of many sep- 

 arate brilliant points. 



Second, the paths are broad, several degrees in width. 



Third, the inner margin is rather sharply defined; there is 

 no such clear outer limit. 



Fourth, the path nearer to the sun is brighter — the separate 

 points of light are visible twice as far away as those in the 

 nearer path. 



Fifth, while the general glimmer of the snow is apparently 

 colorless, the points which lie in the paths glow most brilliantly 

 with prismatic colors ; blues pure and clear as the bluest sky, 

 greens as delicate as the emerald, reds as glowing as the fiery 

 opal. With a movement of the head which brings a blue crys- 

 tal towards the inner edge of the path, its color passes through 

 all the tints of the spectrum ; a movement in the other direc- 

 tion reverses the succession of colors. Within the limits of 

 the path, the colors at first seem to be scattered promiscuously ; 

 more careful observation, however, leads one to feel that there 

 is a slight tendency in the reds to keep to the inside. 



A large number of measurements with the sextant have made 

 it evident that the angle between the eye, the glowing point, 

 and the sun, is not .only constant as regards all other points 

 of like position on the path but also for varying altitudes of the 

 sun. The supplement of this angle, measured from the part of 

 the greatest brilliancy, is for the nearer path about 46°, for the 

 further path about 22°. Let us call this in general d. 



Without seeking a cause for the condition, it is easy to deter- 

 mine what, nnder this condition, the path must be. The 

 locus of points at which a constant angle is made between 



* Abstract of a paper read before the Beloit College Scientific Association, Feb- 

 14, 1893. 



