Light visible and invisible : a series of lectures delivered at the Royal Institution of Great Britain, at Christmas, 1896 (1897)
Thompson, Silvanus Phillips, 1851-1916, Royal Institution of Great Britain · New York : Macmillan · leaf 141
hat they are crossed, as in Fig. 79, nolight can get through the crossed crystals. The one cutsoff all horizontal vibrations and horizontal componentsof vibration, the other cuts off all vertical vibrations andvertical components of vibration. Hence, when crossed,they produce a dark field. One acts… … Fig. 77. Fig. 78. Fig. 79. which once was common but now is rare and expensive.As imported from the mine in Iceland this spar possessesthe peculiar property known as double refraction :when you look through it you see everything double.Here is a fine specimen mounted in a tube. Look atyour finger…
Light · X-rays
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