6 PHOfO-TELEGRAPHY 



in the section 2, so that a slightly different part 

 of the image falls upon it, the resistance changing 

 to r 2 , and the current at the receiving station to 



- ; simultaneously let the electric lamp (whose 

 Y i 



brilliance has of course changed in the proportion 

 of r\ to r 2 ), shine on section 2 of the receiving 

 screen. If you can imagine this procedure to be 

 carried out over the whole photograph at the send- 

 ing station, the ever-varying electric lamp being 

 shone on always corresponding sections of the 

 photographic paper at the receiving station, the 

 movements being in all cases synchronous, you will 

 be able to see that on developing the sheet of papei 

 a photograph would be obtained, consisting of a 

 thousand square patches of different intensity, 

 which, examined from a distance, would give a 

 representation of the original image projected on 

 the screen. Such a process would in practice be 

 both absurd and impossible, but it enables one to 

 form some conception of the idea of Bidwell and 

 Ayrton and Perry. 



The image to be telegraphed could quite easily 

 be a photograph printed on a transparent material, 

 such as celluloid, and this print fixed to a revolv- 

 ing glass cylinder, inside which was fixed an 

 electric lamp, whose rays were concentrated so as 

 to pass through one spot on the cylinder to a fixed 

 selenium cell. On then revolving the cylinder 



