36 MAGIC LANTERN WITH DIRECT CURRENT [CH. I 



upon the screen at the same time. For example, to show falling 

 snow, in one of the lanterns is a slide showing a landscape, city 

 street, etc.. in another is a black band with irregular perforations 

 of minute size which give the appearance of snow-flakes. If now 

 the light in the lanterns is properly regulated, and the black 

 perforated band is moved up over the face of the condenser, 

 the snow-flakes will appear to fall either gently or rapidly in the 

 landscape or street as one moves the band slowly or rapidly. One 

 can give the appearance of a driving storm by tilting the black 

 band, for this will make the flakes seem to fall obliquely. 



For rain effects the black band should have slit-like perforations. 



MOVING SLIDES FOR SINGLE LANTERNS 



47. "Effects" with single lanterns. The appearance of 

 movement may also be produced in a single lantern. For this two 

 slides must be superposed, and one moved over the other. By 

 this means various combinations of designs may be made, and also 

 appearances of relative movement. Here, naturally, the two 

 slides must be close together, or one will be too much out of focus. 

 Special slide carriers are constructed for showing these single- 

 lantern "effects." 



For simple experiments use a single slide-carrier. The slides 

 should have no cover-glass, but may be varnished. Then one 

 slide is put in place as for an ordinary exhibition, and another is 

 inserted over it and pushed by the fingers into different positions 

 to show various combinations. For this experiment the bellows 

 between the slide-carrier and the objective should be removed to 

 give freedom to the hands in making the various changes necessary. 



48. "Slip-slides" for optical deceptions. Slides with lines 

 at various angles, etc., are used to demonstrate these. The lines 

 can be shown separately, and then by pushing one slide over the 

 other one can get various combinations. For suggestions as to 

 slides the reader is referred to works on physiology and experi- 

 mental psychology under "optical deceptions." 



49. Most of the "effects" produced by the movement of two 

 slides over each other, and the use of multiple lanterns are so far 



