io PHOTO-TELEGRAPHY 



get the maximum amount of current that could be 

 obtained at the receiving station one -twentieth of 

 an ampere ; with '05 ampere and only therefore 

 5 watts, it would be almost impossible to actuate 

 a graving tool, even to cut into some soft composi- 

 tion. Block -making is so rapidly done in a 

 modern illustrated newspaper office that such a 

 method is not now worth following up. 



Turning next to Caselli's pan-telegraph, we find 

 him employing a sheet of metal with a sketch or 

 writing drawn upon it in insulating ink ; the sketch 

 on metal was stretched over a curved copper plate, 

 and a similar curved plate was placed at the receiv- 

 ing station, a sheet of paper moistened with 

 potassium ferricyanide solution being stretched 

 over it. The plates were electrically rocked, 

 synchronism being obtained by means of a pen- 

 dulum. A metal stylus traced over the sketch at 

 one end and over the paper at the other, the circuit 

 being completed through the metal plates. At the 

 end of each " rock " the paper and sketch were 

 shifted laterally, so that in each case the stylus 

 travelled over a line parallel to the last line traced. 

 When the sending style touched the metal the 

 current flowed and the ferricyanide was decom- 

 posed, a blue mark being produced. Some excel- 

 lent transmissions of writing, etc., were obtained 

 in this way at a comparatively high rate of speed. 

 The same system was employed by the French tele- 



