The art of projecting. A manual of experimentation in physics, chemistry, and natural history with the porte lumiere and magic lantern. (1892)
Dolbear, A. E. · Lee and Shepard · leaf 141
126 THE ART OF PROJECTING. DOUBLE REFRACTION. A piece of calc spar will be needed to show this. Its size is not very material, though the thicker it is the farther apart will the refracted figures be. It should have smooth faces, but the natural faces are often good enough to permit this phenomenon… … Make a hole a quarter of an inch in diam^tef through a bit of cardboard (unless you chance, w^have a dia¬ phragm with holes of various sizes) ^lid^place it at the aperture ; the small beam ofi^ight which comes through it should be directed Wrizontally upon the screen. Next place the piece x>f spar…
Light · Magic Lantern
Internet Archive · Public domain (published before 1931). Free to use for anything.
