170 TRANSACTIONS OF THE [APR. 1, 
optical constants of any bodies at the temperature of incan- 
descence. 
The similarity between a body emitting light by incandescence 
and a body emitting light by fluorescence was first suggested to 
me by Professor Rood. According to Tait the phenomenen 
of fluorescence is confined mainly to the surface layers. What- 
ever the cause, then, of polarization by emission, the light coming 
from a fluorescent surface ought to be polarized in the same 
way as the light coming from glowing platinum. 
Experiment showed this conclusion to be entirely correct. 
The polarization seen in the uranium glass was similar in every 
respect to that observed in incandescent porcelain, being scarcely 
discernible at any angle less than 50°, but becoming quite 
marked between 85° and 90°, and evidently reaching a maximum 
at grazing emergence. : 
That this polarization was not due to diffusing particles on the 
surface was certain for three reasons. Ist. The surface was NoT 
a diffusing surface except to an exceedingly small extent. 
2d. The light which exhibited the phenomenon of polariza- 
tion was the characteristic yellowish-green light which uranium 
emits, and not the blue light which fell upon the surface. 
3d. The reflecting particles on the surface would have pro- 
duced a polarization in the diffusing plane, 7. e., in the plane de- 
fined by the direction of the beam which entered the instrument 
and the direction of the incident beam, which was in this case 
normal to the surface. As a matter of fact the polarization was 
in a plane perpendicular to this plane. 
Here, then, was an instance of polarization by emission in 
which the surface was perfectly definite and at the same time 
the optical constants of the substance could be easily and ac- 
curately determined. 
