166 Prof. Magnus on the Polarization of Heat at 100° C, 



Upon the radiating surface of the tinned-iron vessel a transpa- 

 rent glass plate of 1 millim. thickness was now fastened. It is 

 clear that the temperature assumed by the outer surface of this 

 glass plate was lower than that of the metallic face upon which 

 it was fastened, and from which it derived its heat. Nevertheless 

 the quantities of heat which it delivered are much greater than 

 those radiated from the metal plate. This superior action of the 

 glass cannot be due to its sending out heat from its entire mass ; 

 for it is known from Melloni's researches that glass does not 

 allow heat of 100° C. to pass through. Consequently the su- 

 periority of the glass must be entirely owing to its greater ra- 

 diating-power. 



Table II. — Radiating surface : — transparent glass. 



Radiating 

 surface. 



Horizontal 

 upwards. 



To the left. 



Horizontal 

 downwards. 



To the 



right. 



Analyzing 

 mirror. 



Left 



Horizontal 



Right 



Left 



Horizontal 



Right 



Left 



Horizontal 



Right 



Left 



Horizontal 

 Right, 



Series of experiments I. 



44 



35 



42 



35 



42 



34-5 



44 



35-5 



43 



35-25 



4275 



39-5 



43-5 



35 



42-5 



35-25 



42-5 



34-25 



43-75 



35-5 



43 



36 



42 



35 



43-25 



3475 



42 



35 



42 



34-5 



44 



35 



43 



34-5 



42 



35-5 



Mean of all values with perpendicular surfaces of \ 



reflection J 



Mean of all values with parallel surfaces of reflection. 



Total heat or sum 



Polarized portion or difference 



Percentage of polarized portion 



mean. 



436 



34-9 



42-2 



351 



42-2 



34-4 



43-9 



35-3 



43 



35-6 



42-2 



35-5 



42-8 



35-1 



77-9 



77 

 9-9 



II. 



mean. 

 39-3 

 33 

 427 

 30-2 

 36-5 

 327 

 39-5 

 33-5 

 42-2 

 31-3 

 37-1 

 31-8 



III. 



mean. 



47-25 



36-25 



45-25 



36-3 



45-3 



35-2 



45-41 



36-8 



43-5 



35-7 



43 



35-7 



39-5 



321 



71-6 



7-4 



10-3 



44-95 



35-99 

 8094 

 8-96 

 11-1 



The numbers show that the heat radiated from the glass at an 

 angle of 35° is also polarized, and indeed perpendicularly to the 

 plane of reflection, exactly as with metals. In order, however, 

 to get rid entirely of the notion that radiation had taken place 

 through the substance, the transparent plate was replaced by one 

 made of black perfectly opaque glass. With this the following 

 values were obtained . — 



