. Optical projection : a treatise on the use of the lantern in exhibition and scientific demonstration. lantern by the late Mr. J. is well known, two mirrors have to be fixed so as to meetat an angle which shall be an aliquot part of a circle. Theyare fixed in a tube as at a (fig. 76), and the effect is thatthe phenomena between them are repeated symmetrically all L 146 OPTICAL PROJECTION round the circle as at b. For the lantern, the tube encasingthe mirrors has a lens at each end, as in c, the tube with thepair forming an objective, which takes the place of theordinary one, and foc
. Optical projection : a treatise on the use of the lantern in exhibition and scientific demonstration. lantern by the late Mr. J. is well known, two mirrors have to be fixed so as to meetat an angle which shall be an aliquot part of a circle. Theyare fixed in a tube as at a (fig. 76), and the effect is thatthe phenomena between them are repeated symmetrically all L 146 OPTICAL PROJECTION round the circle as at b. For the lantern, the tube encasingthe mirrors has a lens at each end, as in c, the tube with thepair forming an objective, which takes the place of theordinary one, and focusses in a sliding jacket any object inthe lantern stage. A rackwork slide containing some loosepieces of coloured glass, beads, and other small objects,between two glasses, is usually employed; but a revolvingchromatrope also gives magnificent effects, and ears of beardedwheat or barley or oats, a loosely webbed feather or two, akey, bits of lace, &c, will give interesting patterns. The kaleidoscope requires very special management. Itis placed in the lantern so that the mirrors stand with the. Fig. 76.—Kaleidoscope edges upright like a V, and is focussed on the screen to itsproper slide, or whatever is to be used. The effect, however,is at first a mere nothing—scarcely visible. The lime-jethas now to be raised on the rod for a distance found by ex-periment, but which usually lies between f inch and 1£ disc on the screen brightens up at once; and the lighthas finally to be carefully adjusted, both as to position anddistance, so that all the segments on the screen are illu-minated as equally as possible. Generally the instrumenthas also to be turned or adjusted a very little to the right orleft, to avoid patches of darkness and get the best lantern kaleidoscope entirely depends for success upon ACCESSORY INSTRUMENTS 147 this careful adjustment of the light. The rays, passingthrough the objects, strike rather downwards upon the mirrors,and are again refl
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Keywords: ., bookauthorwrightle, bookcentury1900, bookdecade1900, bookyear1906
