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.
the sensitiveness of the eyes for various colors. Gen¬ 
erally, after looking steadily at a given color, and the 
disk is made suddenly white, the outline of the colored 
part will be seen in a color complementary to the one 
looked at first. Thus, if a square red glass should be 
projected the residual image would be a square green 
one. If a blue one was projected its complementary 
image would be orange, and so on. A great variety of 
such effects are obtainable with various colored pieces 
of glass, or of films of gelatine, by projecting them 
singly, in juxtaposition, or superposed. 
Let disks of white cardboard a foot or two in diame¬ 
ter have partial sectors painted black, with india ink, 
so that the white and black parts alternate four or five 
times in the circumference. This is to be rotated while 
a powerful beam of light falls upon it. The persist¬ 
ence of some of the elements of white light being 
greater than of others, the disk will appear of various 
colors ; purple, green, and yellow being generally well 
A bulb blown upon one end of a small glass tube, 
five or six inches long, answers for this experiment. A 
drop of colored water can be made to enter the tube 
by first heating the bulb a little by holding it in the 
fingers with the open end of the tube a little below the 
surface of the water. A bubble or two of air will be 
expelled, and the fingers may be removed from the 
bulb. As it cools a drop will be driven into the tube, 
and with a little painstaking it can be brought to any 
required place by cooling or heating the bulb. These 
movements can be shown with the porte lumière and a 
single lens, as shown in Fig. 17, or it can be put in


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