The Art of projection and complete magic lantern ... - Yesterday Image

;157follows :—one end of the frame is occupied with a movable ground glass,the opposite end carries the smoked glasses, on the ground glass endplace the design, or sketch, either in distinct black and white or outlineFig 78.to facilitate the speed and working of the design, these may be previouslymade on pieces of glass with hydro fluoric acid, the glass placed over thedesign and the design traced with the acid, the glass is then allowed tostand and the acid will eat itself into the glass, leaving a concavity orgroove ; a number of designs may be so prepared. When complete theyare placed in the outside end of the frame and the point of the sketcherplaced in the grove left by the acid, and so trace at a very fast rate, andwhen the design traced in white on the black ground is enlarged sometwelve to sixteen feet on the screen, it quite astonishes an audience.The Choreutoscope is another mechanical slide depending uponthe failing of the eye to retain the rapid succession of changes. Theidea originated from a Mr. Beale, in the days of the old Polytechnic^