OF RADIANT HEAT THROUGH CRYSTALS. 10? 



The equality of these ratios proves that the rays in both cases 

 possess the same capabiUty of transmission through the same 

 diathermanous substance. 



As long as the direction of the rays was perpendicular to the 

 axis of the crystal^ there was no difference observed, it mattered 

 not how the direction was otherwise altered. The result true for 

 one of these directions, and mentioned in its proper place, was 

 true for all of them. 



Beryl was next submitted to precisely the same examination 

 as that carried out in the case of rock-crystal. 



In the first instance, I permitted the natural rays to traverse 

 the crystal parallel and perpendicular to the axis, and tested 

 their deportment in the manner already described. 



After the full description given of the mode of experiment with 

 rock-crystal, no obscurity can exist about it in the present in- 

 stance. From the observations with beryl, we obtain the fol- 

 lowing values, each of which is the mean of five distinct obser- 

 vations : — 



From these numbers we draw the inference, that the heat which 

 has passed through the beryl in the di7'ection of its axis is trans- 

 mitted through a diathermanous body in a different proportion 

 from that which has traversed the crystal perpendicular to its 

 axis. 



For, of the first-mentioned class of rays, 56 out of 100 are 

 transmitted through the yellow glass, while of the latter class 

 only 50 rays out of 100 pass through the same medium. The 

 calorific rays, in this instance, are therefore to be regarded as 

 qualitatively unlike. 



The difference exhibited itself in a still more striking manner, 

 where the heat, before it entered the crystal (the axis of which, 

 as before, was horizontal), had been polarized in a vertical plane. 

 The following table contains the results of this observation : — 



