. On microscopical manipulation : being the subject matter of a course of lectures delivered before the Quekett Microscopical Club, January-April, 1869. microscopical examination may, however, easily bemade. This salt is the most powerful polarisingagent known. If two crystals are superposed withtheir axes parallel (Fig. 36, a), light is readily trans-mitted; but, if the axes are crossed, as in b, theparts covering each other become perfectly opaqueto transmitted light. This can easily be seen in aslide of the crystals mounted as a microscopicalobje6t, as some of the crystals are sure to be in
. On microscopical manipulation : being the subject matter of a course of lectures delivered before the Quekett Microscopical Club, January-April, 1869. microscopical examination may, however, easily bemade. This salt is the most powerful polarisingagent known. If two crystals are superposed withtheir axes parallel (Fig. 36, a), light is readily trans-mitted; but, if the axes are crossed, as in b, theparts covering each other become perfectly opaqueto transmitted light. This can easily be seen in aslide of the crystals mounted as a microscopicalobje6t, as some of the crystals are sure to be in thisposition. The sky possesses the power of refledting polarised THE SELENITE FILM. 129 light. If the observer stands with one shoulderdiredled to the sun, so that he faces a point 90^ fromit, and looks at a white cloud through a Nicol prism,he will find that the light reflected from the cloudis polarised, and that, as the prism is rotated, thecloud will alternately appear as a white cloud on adark ground and a dark cloud on a light ground. The effe6ls here described may readily be seenwithout the special apparatus of mirrors, &c., byany on
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectmicroscopy, bookyear1
