Bauhaus-Universität Weimar

Optical Projection: A Treatise of the Use of the Lantern in Exhibition and Scientific Demonstration
Wright, Lewis
which form the base of the apparatus ; after which Mr. 
Neilson succeeded in bringing the speaking-boxes into small 
and compact form.1 The wind is supplied to these chests 
(two divisions of one box) by a Y-tube with a stopcock on 
each fork, the trunk of the Y being connected with the 
bellows. Each short rubber tube is furnished with a pinch- 
cock. The reeds are severally mounted upon identical 
bevelled wooden slides, so that any note slides into dovetails, 
and forms for the time the front of its box ; and each is 
mounted with a mirror of silvered glass, f-inch diameter, 
attached to its free end by a small pillar of cork. After being 
fitted with mirrors (which load them), the reeds are fairly 
tuned—excessive accuracy is not required (see g hereafter). 
The reed-boxes are adjustable round vertical axes coincident 
with the vertical diameters of the mirrors, whether the boxes 
are in the horizontal or perpendicular position. One retains 
a perpendicular position ; the other can either be similarly 
placed, or fixed in a horizontal position rectangularly to it, 
being clamped in either by a screw. 
As regards the action of the apparatus, if it be confined 
solely to Lissajous’ figures, the pencil of light might be 
reflected direct to the screen from the second mirror, as from 
a pair of forks. But being desirous of projecting open 
* scrolls ’ also, after Tyndall’s method, and especially in the 
case of ‘ beats,’ I adopted the arrangement shown in plan in 
fig. 140, Omitting all details of focussing, the pencil of light 
from the lantern l is reflected from the mirror on the first 
reed-box, e, to that on the second, e e, and is thence reflected 
1 Dr. Mann’s arrangement was quite different. He used much larger 
boxes or speaking-chambers, with open apertures for the supply of wind. The 
supply-tube came direct from the bellows, with a nozzle at the end contracted 
to about one-third the size of the hole in the reed-box, and ending with a free 
space of half an inch between this nozzle and the hole in the box. Had I 
found his arrangement described earlier, I should probably have adopted both 
it, and the ingenious inventor’s conclusion that it was indispensable ; as it is 
I prefer (perhaps naturally) the smaller boxes as more easily adjusted, and the 
closed supply as more certain and using less wind.


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