. Optical projection : a treatise on the use of the lantern in exhibition and scientific demonstration. ure almost speaks for plates, with apertures of various shapes which carry thefilms, and which before use are blackened, heated, and thencoated thinly with solid paraffin, are laid upon the mouth ofa funnel, whosenarrow end hasan elbow overwhich is strainedthe speaking-tube,the whole beingarranged in a sim-ple frame whichcan be inserted in,or removed from,a sort of box openat one side. Theedge of the funnelis pierced withapertures to allowair to escape fromunder the slots
. Optical projection : a treatise on the use of the lantern in exhibition and scientific demonstration. ure almost speaks for plates, with apertures of various shapes which carry thefilms, and which before use are blackened, heated, and thencoated thinly with solid paraffin, are laid upon the mouth ofa funnel, whosenarrow end hasan elbow overwhich is strainedthe speaking-tube,the whole beingarranged in a sim-ple frame whichcan be inserted in,or removed from,a sort of box openat one side. Theedge of the funnelis pierced withapertures to allowair to escape fromunder the slots in a boardat the plane mir-rors are adjust-able in position, and can also be turned on axes. The nearly parallel beamfrom the condensers, falling on the first mirror, is reflecteddown upon the film; from this it is reflected again to thesecond mirror, and thence reflected out in a horizontal direc-tion, where is adjusted the focussing lens, which focusses thefilm upon the screen. Thus the whole works direct towards theordinary screen, andean all be adjusted before a lecture, which. —Lantern Phoneidoscope 272 OPTICAL PROJECTION is a great advantage. Sometimes a black card or other screenmay need to be adjusted at the side next the screen, to preventany but the reflected rays which form the image from passingthe apparatus; this will suggest itself. The mouth-pieceI have found it advisable to construct as in the section(fig. 143), with a membrane of thin india-rubber across does not interfere with the true sound vibrations,while it prevents the film from being prematurely rup-tured by any actual blast of air winch might result fromunskilful management of the voice. Kecipes for the solutionwill be found in Chapter XX., and a good filmwill often last a quarter of an hour. Besidesthe usual apertures, a hexagonal one should beprovided; for these about two inches in diameteris a good size. The beautiful figures, and thegradual change in colour, make
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Keywords: ., bookauthorwrightle, bookcentury1900, bookdecade1900, bookyear1906
