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. 



SOURCE OF HEAT. 



Argand Lamp (glass chimney), 



Locatelli Lamp, 



Alcohol Flame, 



Incandescent Platinum, 



Brass, about 700°, 



Mercury, about 500° (in crucible), 



Water under 200°, 



Proportion of Light polarized, •}• 



Rays out of 100, polarized by transmission 

 through Mica Plates E. and F. 



29 

 24 

 36 

 40 



17 



6 



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 all 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. 



-f- 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 



