. Optical projection : a treatise on the use of the lantern in exhibition and scientific demonstration. friction-wheelsrolling on opposite edges of the disc, by cranks fitted tothem, actuate two mirrorsmounted on rocking-pivots,over opposite sides of the re-volving table. Mr. G. M. Hopkins, of aNew York, uses two mirrors,each of which is mounted asat m on the middle part of twoparallel strained wires, a b,in the manner first used forother purposes by Professor0. Eood. Two such wireswill impart to a mirror good vibration, if properly strained, and the period may be variedby attaching another wi
. Optical projection : a treatise on the use of the lantern in exhibition and scientific demonstration. friction-wheelsrolling on opposite edges of the disc, by cranks fitted tothem, actuate two mirrorsmounted on rocking-pivots,over opposite sides of the re-volving table. Mr. G. M. Hopkins, of aNew York, uses two mirrors,each of which is mounted asat m on the middle part of twoparallel strained wires, a b,in the manner first used forother purposes by Professor0. Eood. Two such wireswill impart to a mirror good vibration, if properly strained, and the period may be variedby attaching another wire, a b, with loads at the ends w w(fig. 138) to the back of the mirrors, so that it can be variedin angle (as c d), such an alteration altering the period ofvibration. One pair of wires is of course strained verticallyand the other pair horizontally, in parallel planes. Such anapparatus is easily constructed; but it is very difficult to getexact ratios with it, and difficult to arrange for the pencil oilight to clear both pairs of wires. But by far the best, most effective, and most comprehensive. 262 OPTICAL PROJECTION apparatus is one of reeds mounted with mirrors, as shown infig. 139, which I was able to arrange for Messrs. Newton& Co. with the help of Mr. G. Neilson in the speaking partof the apparatus, it being particularly difficult to makeany range of reed-notes vibrate on a closed box of COnve-
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Keywords: ., bookauthorwrightle, bookcentury1900, bookdecade1900, bookyear1906
