142 THE ART OF PROJECTING. 



may be made very much larger, as much as two or 

 three feet in diameter, and the number of holes in- 

 creased. By 

 removing the 

 I mirror m a 

 little farther 

 away the beam 

 can be reflect- 

 ed so as to cov- 

 er the whole 



Fig. 1O8. M ' face of the disk. 



A small toy steam-engine, such as may be bought 

 for a dollar or two, may have a light paper disk fitted 

 for it to turn, but if sunlight be used, care must be 

 taken lest it take fire in the focus of the sun's rays. 



An oxyhydrogen lantern may be used for such work. 

 The objective will need to be removed, and the perfo- 

 rated disk placed so that the most of the light goes 

 through the holes when they are in position, and the 

 unused light cut off from entering the room by black 

 cloth or some other provision. Otherwise it will be 

 used just as with sunlight. 



THE CHROMATROPE. 



This instrument consists of two disks of glass so 

 mounted that they may be rotated in opposite direc- 

 tions. Various designs are painted upon the disks, 

 and fine effects may be obtained by projecting them in 

 the ordinary way with the lantern or the ports lumicre. 

 If instead of using disks of glass, disks are made of 

 wire gauze, perforated tin, or paper or lace, very curious 

 interference figures are produced, and this form is 

 called the eidotrope. 



