106 



KNOBLAUCH ON THE TRANSMISSION 



parallel to its axis ; for while in the former case 1 1 out of every 

 100 incident rays are transmitted, in the latter case only 7 per 

 cent, pass through. 



It is thus proved that the rays in question differ from each 

 other in respect to quality. 



On the other hand, no perceptible difference is exhibited when 

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

 in a horizontal one. 



Experiments conducted exactly as the foregoing, and differing 

 only in the circumstance that the principal section of the Nichol 

 instead of being horizontal was vertical, gave the following 

 values, each of which is the result of seven observations : — 



The numbers of the two columns differ only within the limits 

 of the error of observation. Hence we conclude that calorific 

 rays whose plane of polarization is parallel to the axis of the 

 rock-crystal are homogeneous, whatever be the direction in which 

 they have traversed the crystal. 



Just as little do differences in the properties of the calorific rays 

 which have traversed the crystal parallel to its axis exhibit them- 

 selves, whether the said rays have been polarized in a vertical or 

 in a horizontal plane. 



This is proved by the following table ; the values contained in 

 it are each the result of four single determinations. 



• The different tables cannot be compared in every respect with each other, 

 as they are the results of observations made on different days, on which it was 

 impossible to preserve external conditions perfectly constant. 



