102 



KNOBLAUCH ON THE TRANSMISSION 



plied, the differences observed in the case of the natural rays 

 disappear. 



The deportment of beryl was similar to that of rock-crystal. 

 True, in the case of beryl a greater quantity was transmitted 

 along the crystallographic axis than perpendicular to it; but 

 the proportion, which in the case of the natural rays was as 

 54 : 100, became, when polarized heat was applied, as 70 : 100. 

 The difference between these two numbers is to be ascribed to 

 the irregularity of the mass already alluded to. 



In the case of tourmaline, no difference was observable in the 

 quantity of heat transmitted. The thermoscope exhibited the 

 same deflection, whether the rays were transmitted parallel to 

 the axis or perpendicular to it. 



From this we may conclude, that polarized calorific rays, whose 

 plane of polarization coincides with the axes of the crystals men- 

 Honed, are transmitted in equal proportions in all directions 

 through the mass. 



The Nichol's prism was next turned so that the plane of its 

 principal section lay horizontal, the rays passing through it being 

 therefore polarized in a vertical plane. 



The deflection produced by these rays, after having traversed 

 the brown rock-crystal in a line parallel to its axis, was 9°'68. 

 When however the line of transmission was perpendicular to the 

 axis, the observed deflection was only 7°'03, — the ratio of these 

 numbers is that of 100 : 7^. 



Hence the difference already noticed with the unpolarized rays, 

 not only exhibits itself here once more, but is shown in an in- 

 creased degree. In the case of beryl, the ratio of the quantity 

 transmitted, under the same conditions, parallel to the axis to that 

 transmitted perpendicular to the same, was as 100 : 21. In the case 

 of tourmaline, the proportion was as 1 00 : 2 1 9. The following table 

 contains the results of these and of the former observations : — 



Name of crystal. 



Heat polarized in I MQ+„«ai ra-ne I Heat polarized in 

 horizontal plane. | J^iaturai rays. | vertical plane. 



Proportionate quantities of heat transmitted through the crystal 



— "«' I 'IK 



to the horizontal cry- 

 stallographic axis. 



to the horizontal cry- 

 stallographic axis. 



to the horizontal cry- 

 stallographic axis. 



Brown rock-crvstal. 



Beryl .' 



Tourmaline 



100 : 100 

 100 : 70* 

 100 : 100 



100 : 92 

 100 : 54 

 100 : 158 



100 : 73 

 100 : 21 

 100 : 219 



Difference due to the accidental irregularities of the specimen examined. 



