340 



GENERAL SCIENCE 



audience sees it; that is, a person in the audience sees each second 

 sixteen different pictures standing perfectly still. If the pictures do 

 not stand perfectly still the picture looks streaked. In order to ac- 

 complish this a revolving shutter (731), Fig. 220, is used. The blade 



FIG. 218. 



moves over the picture as the picture moves. The blade and the pic- 

 tures must move together to prevent a streaky look. If the shutter 

 does not cover the picture at the time the picture is moving, streaks 

 from the letters and flashes of white up and down are seen. This 

 phenomenon is called " traveling ghost." 



