1895. ] NEW YORK ACADEMY OF SCIENCES. 163 
Silver.—Polarization strong, larger for small incidences that in the case 
of platinum. 
Gold.—Polarization strong ; similar to platinum, but apparently less for 
large angles. 
Copper.—Polarization weak, probably due to roughening of surface 
through oxidization. 
Brass.—Polarization weak—( oxidization). 
Tron.—Polarization weak—(oxidization ). 
SoLips.—Non-metalic—transparent. 
Glass.—Polarization weak ; imperceptible exceptat large angles of emer- 
gence. 
Mica—Polarization weaker than in glass. Surface roughened by heat. 
SoLips.—WNon-metallic—opaque. 
Porcelain—Polarization similar to that produced by glass. 
Black Glass.—Polarization similar to that produced by transparent glass. 
LIQuIDs. 
Mofien Silver 1 Polarization similar to that in solid state. 
Gold /f 
‘¢ Tron.—Polarization strong ; almost as strong as in molten gold. 
Bronze.—Polarization strong ; almost as strong asin molten gold. 
Lead.—Polarization weaker than for preceding metals. ( Difficult to get 
a clear surface). 
Zine.—Polarization weaker than for preceding metals. 
cc 
From these experiments it will be seen, Ist, that the metals 
show uniformly high percentages of polarization so long as the 
surface is non-diffusing ; 2nd, that none of the non-metallic sub- 
stances used produce strong polarization at any angle ; 3rd,that 
the transparency or opacity of a substance has apparently little 
effect upon its power of producing polarization in the emitted 
light ; and, 4th, that any cause which interferes with the perfect 
smoothness and regularity of the surface destroys in large 
measure the polarization. 
We. 
INSTRUMENT EMPLOYED FOR QUANTITATIVE EXPERIMENTS. 
In order to accomplish the second and main object of the re- 
search, it became necessary to devise some means of making ac- 
curate determinations of the relations of the constants of the 
partially polarized beam. In case of elliptic polarization the 
constants are best determined by means of a Babinet compen- 
sator, but this instrument fails entirely for partially polarized 
light. The instrument which has been most employed for such 
work by previous investigators is the Polarimeter of Arago. 
