SCIOPTICON MANUAL. 91 



above the poles in the lantern ; then allow iron filings 

 to fall gently down the funnel, which will appear like 

 large blocks attracted upward by a huge magnet. 



ASTRONOMICAL CARDS. The cards may be cut to the 

 size of the crystal slide, that is 3 by 4 inches, so as to 

 be used in the grooved frame, like an ordinary glass 

 slide. After correctly dotting a constellation of stars 

 (which may be done by the use of theorem paper and a 

 good map of the heavens), pierce the card at the several 

 points, say with a darning needle, which may be made 

 to show stars of different magnitudes by gauging the 

 depth of the insertion. 



To illustrate the Solar System, punches of different 

 sizes might be used and bits of colored gelatine, covering 

 the aperture, might indicate the tints attributed to each 

 member. 



PINHOLE OUTLINES. Cards in shape of glass slides 

 and just thick enough to be sufficiently stiff, may be 

 pricked to show maps, mottoes, figures, diagrams, or any 

 simple illustration. They require but little skill and 

 show very distinctly. 



PERFORATIONS. Two pieces of perforated paper or 

 tin made to slide little by little over each other, in front 

 of the condenser, and modified more or less by the 

 tinters, produce beautiful symmetrical forms in great 

 variety. 



PERSISTENCE OF VISION. Apertures, as in a paper card, 

 when moved rapidly in all directions in the plane of the 

 slide, appear as lines of light on the same principle that 

 a lighted stick waved about produces lines of light. A 

 new slide, called the kaleidotrope, is constructed and 

 hung to exhibit this curious effect. 



