78 PHOTO-TELEGRAPHY 



by Professor Korn is to have a flat string slightly 

 twisted, and the most recent galvanometers have 

 been provided with a collar, which can be turned 

 through a small angle, and this has a micrometer 

 scale to it, so that the angle through which the 

 ribbon is twisted can be accurately determined. 



By using a wide slit in front of the receiving 

 box so that more light is admitted to the receiving 

 drum, with a consequent larger movement of the 

 shadow of the ribbon or string, it is possible to 

 receive the picture direct on photographic paper. 

 This is important, as it saves one operation in the 

 photographic work, and a minute or two fre- 

 quently decides whether a picture can be " got 

 in " an early edition of the paper or not. 



The inertia of the photographic sensitive film 

 plays an interesting part in the more brilliant 

 results obtained direct on sensitive paper. When 

 the wider slit is used the tension of the galvano- 

 meter string is made less so that the shadow 

 will rise to the necessary extent to quite open 

 the slit. As it rises and falls each time there 

 is a current sent through the string, the light 

 is obviously greatest at the moment when the 

 slit is totally uncovered and is least at the two 

 instants when the slit is just a little opened and 

 nearly closed. Now before light can produce a 

 developable effect in a photographic film it has to 

 overcome the chemical inertia of the film, and unless 



