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POPULAR SCIENCE MONTHLY. 



sensitized film, beneath an incandescent lamp, whereby the photo- 

 graphs are impressed or " printed " upon the sensitive surface. This 

 second film in its turn is passed through the various photographic 

 processes. When complete, it is wound upon a spool, and is then 

 ready to be placed in the cinematograph or other machine used in 

 exhibiting the pictures. Here, as already stated, the mechanical 

 arrangements correspond to those employed in taking the negatives. 



The Jenkins Camera, with rotating system of lenses ; capable, in sunlight, of taking one 



hundred pictures per second. 



Thus the pictures, when displayed before an audience, are seen to 

 flash out in the same rapid sequence in which the original scenes 

 were presented to the " eye of the camera." 



A homely illustration may aid the reader in arriving at a per- 

 fectly clear comprehension of this subject. Let us take the case of 

 a man who is slowly walking past a high picket fence and gazing 

 intently at some moving object on the other side of the fence. His 

 view will be interrupted at regular intervals by the pickets as they 

 successively encounter his line of .sight. But if he proceed more 

 quickly a seemingly continuous view of the object in question will 

 be obtained, though rapid alternations in its brightness will be 

 manifested. These effects are due to a well-known cause — viz., the 

 persistence of luminous impressions upon the human retina. Thus, 

 our observer's eye retains for a brief period its impression of each 

 momentary glimpse that is afforded him under the conditions just 

 described ; and the successive visual images become merged into one 



