. Optical projection : a treatise on the use of the lantern in exhibition and scientific demonstration. cturer,especially if he has himself to stand near his lantern, as oftenhappens. The assistant has only to concern himself to havethe next diagram ready in the frame not in use ; and can thenbring it on in place of the other in the twinkling of an eye, or MO OPTICAL PROJECTION the lecturer himself, if standing near, can do it with a touchof his hand. The blank screen is never shown. A singlelantern is often fitted with an arrangement for graduallydarkening down to complete obscuration in fron
. Optical projection : a treatise on the use of the lantern in exhibition and scientific demonstration. cturer,especially if he has himself to stand near his lantern, as oftenhappens. The assistant has only to concern himself to havethe next diagram ready in the frame not in use ; and can thenbring it on in place of the other in the twinkling of an eye, or MO OPTICAL PROJECTION the lecturer himself, if standing near, can do it with a touchof his hand. The blank screen is never shown. A singlelantern is often fitted with an arrangement for graduallydarkening down to complete obscuration in front of theobjective ; and in that case also this carrier is best, becausein one moment, with no possibility of hitch or mistake, theslide can be changed while the screen is dark, and the newone will then emerge out of the darkness. This simple effectis thought by many to be quite as pleasing as the now familiardissolving views. This carrier cannot unfortunately be used with two lanternsside by side, for obvious reasons. In that case perhaps thebest form is that shown in fig. 75, where the inner frame. Fig. 75.—Carrier for Pair of Lanterns travels to and fro in the same way, but can only be in positionwhen pushed in, and has to be drawn back and out for theslide to be changed. There are other carriers, some patented; and any opticianwith a large lantern business can show an assortment, or atleast representations of such from catalogues ; but the aboveare in my opinion the best. 76. Mechanical Slides.—These are of many sorts, and canonly be mentioned here, a very large variety being merely ofa comic character. They seem still to maintain theirpopularity amongst certain audiences, and are worth at leastenumeration, as the effects produced may at any momentfurnish some useful hint for more serious purposes. (See foran example Chapter XV.) SLIDES, CARRIERS, AND EFFECTS 141 Slipping Slides have a portion of the picture painted upon aseparate glass, which can be suddenly drawn along
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Keywords: ., bookauthorwrightle, bookcentury1900, bookdecade1900, bookyear1906
