Light; a course of experimental optics, chiefly with the lantern . between and fromboth surfaces of the glass. At a great angle of incidence,the reflection from the first surface of the glass is as bright,or even brighter than that from the silver surface; showingagain that the comparative intensity or completeness ofreflection from various substances, when polished, differswith the angle of incidence. If a piece of plain glass,instead of looking-glass, be used, we see also that reflectiontakes place, not only when rays encounter the polished 30 LIGHT. [CHAP. surface of a denser medium, as gla
Light; a course of experimental optics, chiefly with the lantern . between and fromboth surfaces of the glass. At a great angle of incidence,the reflection from the first surface of the glass is as bright,or even brighter than that from the silver surface; showingagain that the comparative intensity or completeness ofreflection from various substances, when polished, differswith the angle of incidence. If a piece of plain glass,instead of looking-glass, be used, we see also that reflectiontakes place, not only when rays encounter the polished 30 LIGHT. [CHAP. surface of a denser medium, as glass; but also at thesecond surface, where the rays meet the rarer medium ofthe air. We shall hereafter find that this last kind of re-flection is often the more brilliant of the two. In all cases,reflection is the more copious the greater the angle ofincidence, except in this last kind of reflection. Repeated reflection sometimes produces most beautifuleffects. When two mirrors are inclined together at anangle which is any aliquot part of a circle, or 360°, and. Fig. 19.—Multiple images. the rays from any object pass in a path between them,nearly parallel to the junction, there must be as manyimages (including the object) as the angle is contained in360°. A glance at Fig. 20 will show how this occurs. Twosuch mirrors, or even plain rectangular oblong strips of plateglass, fixed in a tube, with a cap at one end made of twoparallel transverse glasses, between which are loosely con-tained some coloured beads, or other transparent objects. n] THE KALEIDOSCOPE. 31 and with a small hole in the other (closed) end of the tube,form the kaleidoscope of Sir David Brewster. In BarkersLantern Kaleidoscope, the mirrors are of platinized glass,and are mounted with a convex lens at each end; thusmounted the apparatus takes the place of the ordinarylantern objective, and will produce beautiful patterns uponthe screen if a rotating slide containing the fragments ofcoloured glass is placed in
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