Bauhaus-Universität Weimar

The Book of the Lantern. Being a Practical Guide to the Working of the Optical (or Magic) Lantern. With Full and Precise Directions for Making and Coloring Lantern Pictures.
Hepworth, T. C.
placed upon a stand that they can each be turned in any 
required direction. The spectrum is allowed to fall upon 
this system of mirrors, and each one is so turned upon its 
axis that the particular colour which it reflects is thrown 
upon one spot. The collective images of the various 
colours then appears as a white disc. 
The methods thus detailed are all good, but cannot 
readily be applied to the lantern. A way of demonstrating 
the recomposition of light with that instrument lias 
recently been published in America, by Mr. G. M. Hop¬ 
kins, and the following remarks are borrowed from him. 
After detailing the various known methods of recomposing 
light, he says :—“Besides these methods, the spectrum has 
been recombined by whirling or rocking a prism ; the move¬ 
ment of the spectrum being so rapid as to be beyond the 
power of the eye to follow, the retina receiving the impres¬ 
sion merely as a band of white light, the colours being 
united by the superposing of the rapidly succeeding 
impressions, which are retained for an appreciable length 
of time. The engraving shows a device to be used in 
place of the ordinary rocking prism. It is perfectly 
simple, and involves no mechanism. It consists of an 
inexpensive prism, having attached to a knob on either 
end a rubber band. In the present case the bands are 
attached by making in each a short slit, and insert¬ 
ing the knobs of the prism in the slit. The rubber 
bands can be held by inserting two fingers in each and 
drawing them taut. The prism can then be held in a 
beam of sunlight, and with one finger the prism is given 
an oscillating motion. The band of light thus elongated


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