Third Series. — Depolarization of Heat. 



109 



be at 0° or at 90° as its plane of refraction is vertical or 

 horizontal. With these explanations, and a reference to art. 

 71, First Series, the following specimens of observations will, 

 it is hoped, be intelligible. 



Argand lamp: 16 inches from centre of pile, depolarizing 

 mica plate No. 3. 



The following experiment was made with heat wholly un- 

 accompanied by light, and with the same mica plate. 



Dark hot brass : 14 inches from pile, depolarizing mica No. 3. 



* Omitted in the mean as manifestly too small, arising from the lamp 

 being just lighted, and the brass not fully heated. 



