ii4 PHOTO-TELEGRAPHY 



dead beat, for example the action would be 

 longer in time than the duration of closing of the 

 circuit at the transmitting end. 



The records made with the recording apparatus 

 already described show that when currents are 

 transmitted through a line with considerable capa- 

 city the " teeth " widen,, and are inclined one to 

 run into the next. This effect is in accordance with 

 the results obtained on the telectrograph, which 

 forms a useful and very sensitive recording appa- 

 ratus in itself. When a series of short contacts 

 are made on the transmitter these should produce 

 short marks at the receiver, but the actual effect 

 is that one mark runs into the next. 



What is required, then, in an ideal system is the 

 shortening up of these elongated impulses, so that 

 the effect in the receiver for current of duration t 

 is also of duration t. This result is obtained to a 

 very fair extent in the balancer already described in 

 the chapter dealing with the telectrograph. 



The reader may possibly have thought that the 

 introduction of the above matter was needless in 

 treating the subject of photo -telegraphy, but the 

 leakance of long-distance lines and their capacity, 

 and the attenuation factor, are the three things 

 which chiefly decide the question : How far and 

 how quickly can photographs be telegraphed ? 



The receiving apparatus destined for the best 

 work between two places A and B is usually of a 



