110 



KNOBLAUCH ON THE TRANSMISSION 



The examination of tourmaline led to the same results as those 

 observed with the other crystals. The results of the observations 

 with natural rays are contained in the following table: each 

 number is the mean of five distinct determinations : — 



The comparison of both series shows plainly in how different 

 degrees the rays which pass parallel to the axis, and those which 

 pass perpendicular thereto, penetrate the same diathermanous 

 body. The former rays pass through the red glass in greater 

 quantity than the latter ; while, in the case of green glass, the 

 latter rays have the preponderance. 



In the same manner, but in an increased degree, these differ- 

 ences show themselves w^hen the calorific rays are polarized in 

 a vertical plane and transmitted through the tourmaline with its 

 axis horizontal. The following greatly divergent values place 

 this beyond all doubt : — 



The differences disappear in this case also when the plane of 

 polarization is horizontal, that is, when it is parallel to the cry- 

 stallographic axis. This is shown by the following numbers, 

 whose difi'erences lie within the limits of the error of obser- 

 vation : — • 



Diathermanous bodies. 



Red glass .. 

 Green glass 



Ratio of the quantity of heat which, polarized in a hori- 

 zontal plane, falls upon the diathermanous body, to that which 

 passes through the latter, having previously traversed the 

 tourmaline 



Parallel | Perpendicular 



to the horizontal crystallographic axis. 



100 : 19 

 100 : 9 



100 : 16 

 100 : 10 



