66 PHOTO-TELEGRAPHY 



screw S ; TT is the finely-drilled tube into the ends 

 of which the needle points fit. Steel needles, sharply 

 pointed, are at present in use in these holders, and 

 the tension is set such that the point does not scratch 

 soft lead foil when attached to the drum. 



These remarks regarding the stylus apply to the 

 Daily Mirror machines, a somewhat different 

 arrangement being employed by Professor Korn. 

 The mechanism of the stylus is, however, a matter 

 of the greatest importance, as is also the shape of 

 its point and the angle that it makes with, the surface 

 of the drum. 



The sparking at the point of contact of stylus 

 with copper foil sketch may be almost overcome 

 by shunting across it a condenser of about i to 1*5 

 microfarad capacity ; the extent of sparking is pro- 

 bably dependent to some extent on the self-induc- 

 tion of the line and may not therefore be always 

 equal. Sodium sulphate cells have been used by 

 Korn with great success also. 



A battery of from 30 to 60 volts is usually 

 employed at the sending station, and the amount 

 of current received at London from Paris averages 

 between 6 and 1 2 milliamperes ; from Manchester 

 between 9 and 18 milliamperes. 



The function of the transmitter is clearly to send 

 an electric current to the receiver, which is broken 

 constantly, the duration of the brakes depending on 

 the width of the shellac lines of which the sketch 



