TELEGRAPHING. 179 



the other plate the other pole of the condenser. The condenser is a 

 block to the passage of the primary currents from the telegraph wire, 

 but permits the passage of secondary currents by induction. The con- 

 denser I'enders it possible to superimpose induced currents upon tele- 

 graph wires without interference, and the use of the condenser renders 

 simultaneous telephony and telegraphy not only possible but prac- 

 ticable. Turning to the question of priority of invention, he doubted 

 not the members ot the Canadian institute would receive the an- 

 nouncement with satisfaction when he stated that the so-called " air 

 telegraph " was largely a Canadian invention. The facts are as fol- 

 lows : — In SeptemV)er, 1877, a private telephone line was constructed 

 in this city from King street up Church street to Charles street. 

 This was before the magneto signal bells were introduced, and as 

 there was no battery upon the line until some time after the line was 

 constructed, it was necessary to devise other means for signalling. 

 This resulted in the adoption of the ordinary Faradic medical battery 

 for the generator, and the telephone diaphragm for the receiver. 

 This was called the " buzzer," as it gave a buzz or humming sound in 

 the telephone. . A. naonth or two later a telegraph system was de- 

 vised in Toronto on this pi-inciple, namely, using an induction coil, a. 

 vibrator, a local battery and key as a transmitter, and a magneto- 

 telephone as a receiver. In the spring of 1878 Mr. George Black 

 of Hamilton made the important discovery that a telephone circuit 

 ni-r-y be established through an electrical condenser. This at once 

 opened tlie way for using the telephone and other telephonic ap-, 

 paratus as a duplex on the ordinary telegraph wii-e, as it was found 

 that by means of condensers an artificial or phantom circuit could be 

 established for the telephone instruments independent of the tele- 

 graph signalling — the condensers acting in a threefold capacity : 

 firstly, they prevented grounding or crossing of the telegraph lines ; 

 secondly, they bridged the interval of the opening of the telegraph 

 key, and thirdly, they suppressed induction. 



This discovery forms the basis, not only of the air telegraph, but 

 also of the Edison duplex " Phonoplex " and " AVay Telegraph," as 

 well as of tlie Van Rysselberghe " Telegraph cimi Telephone " system 

 now in extensive use in France and Belgium. 



In all these cases induced electrical currents are superimposed iipon 

 the telegraphic circuit by means of condensers and both tlie primary 



