TRANSACTIONS OF SECTION A. 663 
If the angle between the plates is twice the complement of the polarising angle, 
say 67°, no light is reflected when the edge of the V is vertical, and therefore this 
angle gives the best illumination. If the angle is about 80°, the strips mentioned 
above have the greatest width. Probably any angle between these values will serve 
almost equally well, and I do not find in practice much difference inefficiency with 
different angles. 
The device acts well for projection with a lantern if very thick plates are used. 
