Second Series. — Polarization by Refraction. 359 



22. These are given as examples of the usual mode of pro- 

 ceeding with such experiments, the zero point being ascertained 

 between each observation, and the dynamical effect reckoned 

 from it. On the whole, I obtained for the proportion of heat 

 polarized, or stopped in the transverse position of the plates, the 

 following numbers : 



Plates I and K. 





Source of Heat. 



Rays out of 100, polarized 



Argand Lamp, ....... 



72 to 74 



Incandescent Platinum, ...... 



72 





63 



Heat from the same source transmitted through glass, 



72 



Mercury in a crucible at 410°, .... 



48 



Boiling Water, ....... 



44 



Plates G and H. 





Argand Lamp, ....... 



82 



Incandescent Platinum, ..... 



79 



Brass heated to about 700°, ..... 



68 



Heat from the same source transmitted through glass, 



73 





49 



It thus appears that the Plates G and H are capable of polarizing 

 no less than 82 per cent, of some kinds of incident heat : these 

 plates I began to use in the commencement of December last. 



23. The unequally polarizable nature of different kinds of 

 heat having been controverted, I took several methods of as- 

 suring myself that the observed effects were not due to in- 

 equalities in the dimensions of the sources of heat employed, or 

 to their variable distances from the pile. A multitude of proofs 

 might be given, but I will content myself with stating one or 

 two of the most decisive. 1. Incandescent platinum and dark 

 hot brass were successively placed at the same distance of twelve 

 inches from the pile ; a thin plate of glass being placed between 

 the latter and the pile, and two thick plates of glass between the 



VOL. XIII. PART II. 3 N 



