. Optical projection : a treatise on the use of the lantern in exhibition and scientific demonstration. light of any diameterfrom 16 mm. downwards can be obtained with the 0. H. rays will of course scatter or diverge considerably, evenwhen parallelised as far as possible ; but in acoustical pro-jections this is an advantage rather than otherwise. Such a pencil attachment has another use. By removingthe concave paralleliser (which should be removable) a strongconical pencil can be thrown through a very small hole, in 174 OPTICAL PROJECTION whose diverging rays large shadow projections w
. Optical projection : a treatise on the use of the lantern in exhibition and scientific demonstration. light of any diameterfrom 16 mm. downwards can be obtained with the 0. H. rays will of course scatter or diverge considerably, evenwhen parallelised as far as possible ; but in acoustical pro-jections this is an advantage rather than otherwise. Such a pencil attachment has another use. By removingthe concave paralleliser (which should be removable) a strongconical pencil can be thrown through a very small hole, in 174 OPTICAL PROJECTION whose diverging rays large shadow projections will be welldefined, as described in Chapter XIV. Such an attachment can either be fitted into the jacket c dof the optical front (fig. 94), or if the back lens be made oflonger focus, it may simply be fitted into the small end nozzlen of that piece of apparatus. 89. Optical Accessories.—For general focussing and otherpurposes there should be provided, wherever physical demon-stration is attempted, at least two rod or pillar stands, madeby screwing a half-inch brass tube into a heavy foot, covered.
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Keywords: ., bookauthorwrightle, bookcentury1900, bookdecade1900, bookyear1906
