Bauhaus-Universität Weimar

Optical Projection: A Treatise of the Use of the Lantern in Exhibition and Scientific Demonstration
Wright, Lewis
under pressure. A two-necked glass receiver, as shown in 
fig. 148, will answer very well, blacked all over except for a 
circle of four inches diameter opposite one orifice. This is 
supported as at a. The orifice is a short piece of glass tube 
fixed in cork, upon which the light will be condensed. Several 
feet higher the supply of water must be placed (a bucket will 
suffice) connected with the receiver by the tube b, and the 
receiver is filled. On withdrawing a cork from the glass tube 
at the orifice, the water will issue in a smooth stream, when 
the radiant can be adjusted to give the best effect. Various 
colours can be imparted to the stream by placing different 
coloured glasses in the slide stage of the lantern. 
Instead of this primitive apparatus, a vessel of tin, with 
one glass side to go against the lantern flange, and an orifice 
opposite, may be constructed. Such a vessel will be supported 
more steadily, and the light can be more precisely adjusted 
through a plane glass ; while the pencil attachment shown 
in fig. 95 may be used to give more brilliance. 
159. Prisms and Lenses.—The permanent deviation of a 
ray or beam of light 
by a prism is best 
shown by placing a 
small aperture in 
black card or metal 
in the stage and 
focussing on the 
screen (or a hole in 
the plate of aper¬ 
tures focussed by 
the loose lens will 
do equally well), and 
interposing in the 
path of the rays a thin prism, often called a wedge prism, 
which will show no conspicuous colour. Such a prism may 
be made by cementing a wedge-shaped glass cell, and filling 
Fig. 14J.—Spectrum


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