90 THE ART OF PROJECTING. 



good illumination. By removing the objective the dia- 

 phragm of black paper can be removed. As the 

 objects are all magnified so much, it will be found that 

 quite small bits of colored glass will look better than 

 large ones. 



2d. With a lantern. 



It will be observed that the essential condition for 

 showing the kaleidoscope with the porte lumiere is, 

 that all the light that reaches the screen must be the 

 light that is reflected from the inclined mirrors, and 

 that the focus of the converging beam must fall just in- 

 side the outer end of them. Hence the focus needs to 

 be as small as possible for the best effect. With the 

 lime light the focus is quite broad at its narrowest 

 part ; therefore when the kaleidoscope is placed in the 

 beam it will be necessary to adjust the light by raising 

 it, so that the reflectors receive all of the light, and it 

 also may be necessary to draw it back a little that the 

 focus may come to the proper place. 



The ordinary objective upon the lantern will not 

 be needed, of course ; but an objective having a focal 

 length equal to or a little longer than the length of the 

 kaleidoscope may be used, holding it in a retort 

 holder or in any other convenient way. Let as much 

 as possible of the extraneous light be excluded from 

 the room by black cloth about the front of the lantern. 

 With these precautions a very good projection of ka- 

 leidoscopic forms can be shown. Even with the better 

 forms of the oil lantern it is possible to project them 

 quite well. As the diameter of the disk is doubled 

 with this fixture, it will be necessary to move the 

 lantern much nearer to the screen. 



