398 



Intelligence and Miscellaneous Articles, 



ON THE PASSAGE OF THERMAL AND LUMINOUS RAYS THROUGH 

 INCLINED DIATHERMANOUS AND TRANSPARENT PLATES. BY 

 H. KNOBLAUCH. 



On the occasion of an investigation instituted by the author in the 

 year 1847 on the polarization of heat by simple refraction*, he had 

 observed that solar rays traversed a number of parallel glass plates 

 which originally were placed at right angles to them, the more copi- 

 ously the more they were inclined, which was the more surprising as 

 with an increasing thickness of the layer a diminished intensity 

 would rather have been expected. 



This increase was still further increased if the thermal rays reach- 

 ing the glass through a Nicol's prism were polarized in such a man* 

 ner that their plane of polarization was at right angles to the refrac- 

 tive index of the glass plates. If, for instance, a Nicol placed in a 

 window was horizontal, and hence the plane of polarization of the 

 rays passing through vertical — if, further, the upright glass plates were 

 moveable about a vertical axis, the horizontally refracted thermal rays, 

 caught completely at each inclination of the glasses on a thermopile, 

 produced the following deflections on a multiplier connected with it:— * 



Angle which the 



thermal rays 



formed with the 



normal to the 



glass plates. 





 20 

 40 

 60 



Deflection on the thermomultiplier on the 

 passage of the heat-rays through 



8 plates. 6 plates. 9 plates. 12 plates 



1600 

 17-25 

 1725 

 19-50 



10-50 

 11-50 

 1300 

 13-75 



700 



8-00 



10-25 



1200 



4-50 

 4-50 



8-75 

 10-50 



Although these observations had not the object of ascertaining 

 those transmissions, and were not made in a series to be comparable 

 for the present case, they prove beyond doubt that, at all events 

 within wide limits,— 



I. The capacity of thermal rays of traversing parallel glass plates 

 increases with the angle which they form with the normal to the glass 

 plates. 



II. This capacity increases with the number of plates. 



If, owing to a rotation of a Nicol's prism through 90°, the plane of 

 polarization of the rays entering coincided with the refractive index of 

 the piece of glass, the heat which passed through produced the fol- 

 lowing actions on the thermoscope : — 



Angle which the 



thermal rays 



formed with the 



normal to the 



glass plates. 



Deflection on the thermomultiplier on the 

 passage of the heat-rays through 



3 plates. 



6 plates. 



9 plates. 



12 plates. 



o 





 20 



40 

 60 



16-00 

 16-00 

 12-75 

 10 25 



10-50 

 10-50 



8-00 

 4-00 



7-00 

 6-37 

 5-00 

 1-00 



4*50 

 2-37 

 237 

 0-00 



Poggendorff's Annalen, vol. Ixxiv. p. 170. 



