Bauhaus-Universität Weimar

The Art of Projecting. A Manual of Experimentation in Physics, Chemistry, and Natural History with the Porte Lumière and Magic Lantern
Dolbear, A. E.
number of circular crystals will be formed with radiat¬ 
ing forms between them. These circular crystals may 
be made larger and regularly disposed by touching the 
mass with a fine needle point when crystallization 
begins. Such ones will form about each point touched. 
Magnify such objects so much that these circular 
crystals will appear a foot in diameter upon the screen. 
The Nicol’s prism will show each one with four arms 
that will turn about the centre of the crystal when the 
prism is rotated, while the radiating crystals will show 
as red, yellow, or purple brushes sweeping over the 
By inserting a sheet of transparent mica or thin 
selenite between the reflector and the object, a colored 
field will appear as a kind of background, upon which 
the minute crystals, such as chlorate of potash and 
oxalic acid, will appear more highly colored. The effect 
is usually to heighten the color. 
Fig. 103• 
With a large lens project the image of the aperture 
upon the screen, the light being polarized by the black¬ 
ened reflector. At the focus of the lens place the 
prism. Two images of the aperture will appear and


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