IN PLATES, TUBES, AND CYLINDERS OF GLASS. 369 
4 
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 Plates, Distance of Extre- Thickness of Breadth of the Maximum 
or AB. 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 0.1383 of an 
inch, and breadth 0.33. One of these broke when the tint was 
10.4, another when the tint was 12, 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. 
Vox. VIII. P, Il. 3A ...- The 
