and Polarization of Heat. 151 
43. With argand lamp, and glass chimney; Plates E and F : 
ratios, 100 : 70 ; 100 : 72; results very steady. 
44. When we combine these results *, and compare them 
with the quantity of light polarized, which was derived from some 
rude photometrical experiments, which agreed pretty nearly, we 
get the following approximations to the degrees of polarization, 
by a given combination, and depending on the source of heat. 
Rays out of 100, polarized by Tan 
SOURCE OF HEAT. Se 2s a lectees by tras 
Argand Lamp (glass chimney), : : : ‘ 29 
Locatelli Lamp, A ; : 5 é ; ; 24. 
Alcohol Flame, : F : 3 : : . 26 
Incandescent Platinum, . P : f : ; 40 
Brass, about 700°, . F F 4 ; F 22 
Mercury, about 500° (in enaetbley? : : : : 17 
Water under 200°, ~ , = 4 : 6 
Proportion of Light polarized, + 5 : : : 89 
45. So completely and satisfactorily made out does the pola- 
rization of heat appear by these concurrent experiments, that it 
was little more than a matter of curiosity to verify it in the case of 
reflection from surfaces, as well as in that of transmission through 
plates. This, however, I also established, though not without 
much more trouble than the other, the change of direction of the 
ray by reflection presenting a troublesome necessity for making 
the thermometric instrument, that is, the pile, moveable; at 
least, this was the most unexceptionable method. I fully esta- 
* It should be remarked, that these experiments contain al/ the measures I have 
made with a view to this determination, except two, which were made the very first 
day I discovered the fact, and which were not accurate enough to be employed. I 
mention this, because, in such experiments, it is important to be assured of the con- 
stancy and marked nature of a result, which can only be appreciated by keeping 
back no fairly made observation. 
+ Though I am not aware of any source of error, I cannot help thinking, that, 
in this case, and in that of the tourmaline, Art. (21.), the defalcation of light is esti- 
mated too high. 
7 
