. Optical projection : a treatise on the use of the lantern in exhibition and scientific demonstration. fig. 70, the poles being built of three short pieces connectedby tubular sockets on the ends, so thatthe stand for a twelve-feet screen willpack into a case about 4| feet long bysix inches square. These stands areto be had fitted with pulley-rollersat each corner, when they are equallysuitable for either a sheet or a paper-faced screen ; the latter being simplyhung, while a sheet is first strainedover the pulleys, and then laced to thepoles by twine or tapes. FlQ. 70 Another simple plan for
. Optical projection : a treatise on the use of the lantern in exhibition and scientific demonstration. fig. 70, the poles being built of three short pieces connectedby tubular sockets on the ends, so thatthe stand for a twelve-feet screen willpack into a case about 4| feet long bysix inches square. These stands areto be had fitted with pulley-rollersat each corner, when they are equallysuitable for either a sheet or a paper-faced screen ; the latter being simplyhung, while a sheet is first strainedover the pulleys, and then laced to thepoles by twine or tapes. FlQ. 70 Another simple plan for elevatinga roller screen, is to provide four pieces of pine-wood, each7 feet or more long, and about 3x1 inches in section. Quarter-inch holes are bored every three inches for a couple of feet fromeach end, and four bolts with flange nuts are provided. Thentwo of the pieces can be clamped together by two of the bolts,so as to make one prop, and these props can either be simplystood on end and secured by guy-ropes, or may be fitted intobase-pieces, or may be furnished with buttress pieces at the e2. ly- OrTICAL PROJECTION bottom. The top roller of the screen itself keeps them theproper width apart. A tracing-paper screen is always furnished with a portablestand, so constructed that if necessary it can be placed upona table. Transparent calico screens are usually stretched acrossthe space occupied by folding doors. This is easily done bylacing twine lightly to large tacks, or even stout drawing-pins,which can be removed without leaving any conspicuous sign. 71. Light for the Lecturer.—Most of the opticians supplya sort of fold-up desk, which shades the light from all but thecopy of the lecture ; but such apparatus is now out of date, being superseded by a simple lamp. Ifthis ig properly shaded, somewhat as infig. 71, which is a pattern very widelyadopted in general, with little variationsin detail, all necessary purposes will beequally secured, and some sort of deskor table can
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Keywords: ., bookauthorwrightle, bookcentury1900, bookdecade1900, bookyear1906
