Light; a course of experimental optics, chiefly with the lantern . o the edge of which is driven a shortlength of tube, c, fitting intothe socket tube b c (Fig. 6).Or if there is no lathe atcommand, the hole may be cutwith a fret-saw, and the lensfixed with short pins each can of course be mounted J- in brass if preferred; but- . .i in that case it is well, when III using, to put round it a border of black card, to exclude from° the screen all but the rays focused. A lens of 3 inchesdiameter and 7 inches focus is a good sort, and a meniscus,with the concave side to the screen, is to be
Light; a course of experimental optics, chiefly with the lantern . o the edge of which is driven a shortlength of tube, c, fitting intothe socket tube b c (Fig. 6).Or if there is no lathe atcommand, the hole may be cutwith a fret-saw, and the lensfixed with short pins each can of course be mounted J- in brass if preferred; but- . .i in that case it is well, when III using, to put round it a border of black card, to exclude from° the screen all but the rays focused. A lens of 3 inchesdiameter and 7 inches focus is a good sort, and a meniscus,with the concave side to the screen, is to be preferred wherethe expense of an achromatic lens is an object; but twolenses of 6 inches and 10 inches are very handy, according aswe may want to enlarge and collect all the light we can froma small object, or to focus a large one. Quarter-inch tubeis a good size for these accessories, but a gauge should bechosen which can always be matched, and the socket B c(Fig. 6) made to fit. In fact, a foot or two of tube to mountany apparatus should always be at hand. I. I-] ACCESSORY APPARATUS. i; A reflector, say 6 inches by 4 inches, of good thin looking-glass, may be mounted as in Pig. 8. d b is a length of thetubing, D c fitting into the socket. From a to b half the tubeis filed away, with a notch at c, into which one long edge ofthe glass fits. The b end is still further filed away; andwhen the glass a b is put in position, with a strip of cardor blotting behind and round the bearing edges, to impart Fiu. 8 a little give, the end b is brought over, and b and c gentlypinched down. The half-tube will keep it nice and reflector may be also mounted in other ways, and forsome experiments a second one is handy, but seldom reallyrequired. A glass prism, 2 inches long, and about ij inches inface, of good dispersive power, can be bought for about
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Keywords: ., bookcentury1800, bookdecade1880, bookidcu3192403121, bookyear1882
