Electric Cinematograph. 63 



where about 1835 the management of the Polytechnetic 

 Institution of London introduced into their exhibition an 

 invention of Dr. Paris called a thaumatrope. This was quickly 

 superseded by another called the phenakistascope or wonder 

 turner. The Instrument that was shown upon the^^screen was 

 made by Dubose, the optician, of Paris, from details supplied 

 by the inventor, Plateau, who was a blind man. In this there 

 was a disc of glass, on which was painted the picture in a series 

 of stages, and also a wheel having a number of lenses on the 

 edge, and as those were made to revolve the pictures and lenses 

 met opposite the tube when the picture was projected on the 

 sheet, and as those must coincide the mechanism had to be 

 very carefully made. The circle and pictures in one form of 

 this device was below the slits, and to use it it was necessary to 

 stand before a mirror and look at the reflected image through 

 the slits, and make the disc revolve when the circle of pictures 

 all seemed in motion, but should they look over the edge no 

 pictures would be visible, only a confused series of eccentric or 

 circular blurs. That was due to the well-known law of the 

 persistence of vision, and it was that law which made it possible 

 to construct those instruments at all. Most of the audience 

 knew that any changes occurring at a greater speed than about 

 eight in a second the eye could not perceive ; so, in order to 

 make the rapid changes visible, they must uiterpose a period of 

 rest or darkness having a certain ratio to the time the object 

 was visible. That proportion he had^not found stated in any 

 text-book, and he had not had anyone to work it out, but he 

 was sure it would -vary in different individuals. Having pointed 

 out some peculiarities about the old familiar zostrope, Mr. 

 NichoU went on to explain that in all those appliances there 

 was a similiarity of design, and as the principle was a fixed one 

 there was little room for change. In the wheel-of-life lantern 

 slide there was a small circle of glass 2f inches in diameter 

 having the figures photographed on it, and another circular 

 plate of metal with one cut in it. When that was made to 

 revolve the figures seemed all to be in motion. He next 



