ELECTROLYTIC RECEIVER 97 



as one must have a paper always conductive, 

 and therefore always in a moist condition, and 

 whilst it is sufficiently absorbent it must have 

 a smooth surface, as otherwise the grain is painfully 

 prominent when the picture is copied for reproduc- 

 tion. The resistance of the paper may be any- 

 thing from 1,000 to 5,000 ohms, and as it 

 must mark instantaneously with a current of about 

 i milliampere it requires to be extremely sensi- 

 tive. The speed at which the paper passes under 

 the stylus is 3*75 inches per second, and since 

 the amount of the element liberated which causes 

 the discoloration is by weight equal to the product 

 of current, time, and electro -chemical equivalent, 

 it is seen that an exceedingly small amount 

 of chemical action takes place. When much current 

 is lost in the line it is sometimes necessary to in- 

 crease the voltage at the sending end. Although 

 only about a milliampere of current flows actually 

 through the paper, twenty or thirty may flow 

 through the line, this excess of course going into 

 the shunt circuit or balancer of the receiver. The 

 secondary discharge of a small induction coil is 

 quite sufficient to mark the paper used, so that the 

 effect of electrolysis can be produced with prac- 

 tically " no current," provided the tension be 

 sufficiently high. 



The first experiments were made with the telec- 

 trograph in 1909 at the Imperial International 



P.T. H 



