. Optical projection : a treatise on the use of the lantern in exhibition and scientific demonstration. termission occasions nodifficulty whatever. Another cut-off jet has been constructed by Mr. plug of the ordinary taps has a screw piercing downthe centre from the top, into the gas-way. The gases areadjusted by screwing these down so as to obstruct or free thepassage, while each tap can be turned entirely off at pleasure,the hydrogen tap having a small channel all round as a bye-pass. The two taps have, however, to be turned separately,and some care is requisite to keep the adjus
. Optical projection : a treatise on the use of the lantern in exhibition and scientific demonstration. termission occasions nodifficulty whatever. Another cut-off jet has been constructed by Mr. plug of the ordinary taps has a screw piercing downthe centre from the top, into the gas-way. The gases areadjusted by screwing these down so as to obstruct or free thepassage, while each tap can be turned entirely off at pleasure,the hydrogen tap having a small channel all round as a bye-pass. The two taps have, however, to be turned separately,and some care is requisite to keep the adjusting screws gas-tight. 64. Tri-unial Lanterns.—By adding a third lantern tothe top of a bi-unial, we get the tri-unial lantern, as in fig. 66, LANTERNS AND THEIR MANIPULATION 119 which shows one fitted with shutter for the curtain effect,(p. 122), and telescopic mounts. In nearly all cases the toplantern is made removable, as here represented, so as to beuseful as a single lantern, and allow the remainder to bepacked lighter, as a bi-unial. With the exception of the dissolving apparatus, there is. Fig. 66.—Tri-unial Lantern little to add about the tri-unial. The object of the thirdlantern is solely to allow of further dioramic effects, with setsof slides made to exhibit such in combination. For instance,dissolving into a snow scene may be done with two nozzles ;but to do so combined with the effect of falling snow, can only 120 OPTICAL PROJECTION be done with three, and is a charming effect. Except for suchextra effects, and for exhibitors who really use these, andknow how to produce them, and can give care and skill toregistering their own stock of slides for them, the triple lanternis a sheer waste of money; and the greater part of those pur-chased are never really utilised. The centre nozzle of a tri-unial is kept square, and thewhole lantern must be first tilted or adjusted by it to thecentre of the screen, and this jet first got in order. Afterwardsthe top and bottom l
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Keywords: ., bookauthorwrightle, bookcentury1900, bookdecade1900, bookyear1906
