RIGIDITY OF SELENIUM CRYSTALS 
105 
distance between the knife edges, and the centering of the point 
of application of the bending force. was employed to measure 
the bend. A and B are the knife edges, the scale pan, and X the 
crystal. The face widths were measured previously to the experi- 
ment by attaching the crystals with wax along the axis of a rod, 
which could be rotated so as to present in succession the six faces. 
Considering only one crystal, No. 6 in detail, as typical of all the 
others, we have in figure 24, drawn to scale, the sections of the 
crystal at the two knife point edges, A and B. The numbers on 
the edges of the crystals are in micra. The detailed results for this 
crystal are given in Table I. 
TABLE I 
Face C above. Crystal No. 6 
Load 
(mg) 
. Reading 
(adding 
load) (mm) 
Bend 
(mm) 
Reading 
(Subtracting 
load) (mm) 
Bend 
(mm) 
pan 
.423 
.288 
400 
.409 
.014 
.277 
.011 
800 
.398 
.011 
.264 
.013 
1200 
.385 
.013 
.250 
.014 
pan 
.425 
.290 
400 
.411 
.014 
.277 
.013 
800 
.398 
.013 
.264 
.013 
1200 
.387 
.011 
252 
.012 
1600 
.376 
.011 
.240 
.012 
pan 
.494 
.357 
400 
.483 
.011 
.345 
.012 
800 
.470 
.013 
.332 
.013 
1200 
.457 
.013 
.322 
.010 
pan 
.493 
.356 
400. 
.482 
.011 
.345 
.011 
800 
.469 
.013 
.334 
.011 
1200 
.457 
.112 
.322 
.012 
1600 
.446 
.011 • 
.312 
.010 
