108 KNOBLAUCH ON THE TRANSMISSION 



I Ratio of the quantity of heat which, polarized in a vertical 

 plane, falls upon the diathernianous body, to that which 

 Diathernian(ni8 bodies. P'""''^ througli the latter, the heat having previously tra- 

 I versed a cube of beryl 



Parallel | Perpendicular 



to the horizontal crystallographic axis. 



Blue glass..., 

 Yellow glass 



100 : 39 

 100 : 54 



100 : 50 

 100 : 30 



In this instance, the difference, as regards the transmissive 

 power of both groups of rays, exhibits itself very distinctly. 

 One group (that parallel to the axis of the crystal) is transmitted 

 in less quantity through the blue glass than the other, while the 

 latter is transmitted through the yellow glass more sparinglj^ than 

 the former. The differences in the present case are, in them- 

 selves, greater than when unpolarized heat was made use of. 

 Thus, in the case of unpolarized heat, out of 100 rays incident 

 on the yellovv glass, 56 were in one position transmitted, and 

 50 in the other position ; but in the present case the numbers 

 corresponding to these positions are 54 and 30. 



All differences of this kind again disappear when the heat, 

 instead of being polarized in a vertical plane, is polarized in a 

 horizontal one. This is manifest from the following numbers, 

 which differ from each other, in both compartments, only within 

 the limits of the error of observation. 



Hence in the case of beryl also, we find that the calorific rays 

 whose plane of polarization coincides with the axis of the crystal 

 are homogeneous, although they may have passed through the 

 crystal in different directions. 



The same similarity of deportment is exhibited by all rays 

 which have traversed the crystal parallel to its axis, whatever be 

 their plane of polarization, Tlie following table contains the 

 observations which refer to this point : — 



