TN PLATES, TUBES, AND CYLINDERS OF GLASS. 



369 



6. On the Intensity and Distribution of the Polarising Force in 

 Plates of Bent Glass. 



In order to ascertain the intensity of the polarising force, as 

 produced by different degrees of flexure, I placed together two 

 similar plates A B, C D, Fig. 13, and separated their extremi- 

 ties by two pieces of glass A C, B D, of equal thickness. After 

 pressing them into contact at M and N, I observed the maxi- 

 mum tints which they exhibited at these points, as given in the 



following Table, 



■ 









Length of Piates, 



Distance of Extre- 



Thickness of 



Breadth of the 



Maximum 



or A B. 



mities, or A C. 



the Glass. 



Plate. 



Tint. 



16 inches 



0.16 



0.133 



0.35 



4 



13 



0.16 



0.133 



0.35 



9 



12 



0.048 



0.207 



0:967 



10.6 



6 



0.054 



0.133 



0.35 



10.5 



With the view of ascertaining the tints which they yielded be- 

 fore they broke, I took plates, whose thickness was 0.13S3of an 

 inch, and breadth 0.33. One of these broke when the tint was 

 10.4, another when the tintwas 1 2, and a third when it had reached 

 13.55. In the phenomena of bent glass, the polarising force is 

 distributed in such a manner, that the lines of equal tint are 

 the lines of equal compression or dilatation, and the tint at the 

 edge is every where inversely proportional to the radius of cur- 

 vature. 



In order to compare the effects produced by the application of 

 the same force to plates of different thicknesses, I placed them 

 as in Fig. 13. The thickness of A B was #133, and its tint 3,4. 



Vol. VIII. P. II. 3 A The 



