9.2 PHOTO-TELEGRAPHY 



mitting to receiving station, say of ^oo^ n secon d 

 duration, and we were to place a piece of chemically 

 sensitive paper on the receiving drum, the latter 

 revolving in the ordinary way, we should get 

 a mark of this form ^^, showing that the line 

 takes an appeciable time tc 

 charge up, and when charged, 

 requires time again to fully 

 discharge. This can be repre- 

 sented by the curve shown in 

 Fig. 42. If we were to transmit 

 several brief currents of equal 



Tim e . 



period, and were then to stop 

 suddenly, we should get a 



continuity of marking, not dying away for an appre- 

 ciable time. 



These difficulties can be almost entirely over- 

 come by the line balance described by me in 

 November, 1909,* in which a current with shunt 

 capacity and an inductance to time the phase 

 where necessary is sent into the line to damp 

 down the secondary surges. The arrangement 

 is seen in Fig. 43. D is the receiving drum 

 and S a platinum stylus. The shunt circuit 

 consists of two similar parts, a secondary 

 cell being in each, BI and B 2 ; a variable induct- 

 ance in each (not shown) ; and a variable resistance 

 of 1,000 ohms, RI and R 2 . The ends of the resist- 

 * Journal of the Society of Arts, 2975, 30. 



