266 



WIRELESS TELEGRAPHY 



Fig. 4. 



-Details of Marconi's transmitting 

 svstein. 



While Dr. Lodge has since done important work in connection with 

 wireless telegraphy, he was, at the time mentioned, presumably more 

 absorbed in the subject from the purely scientific standpoint than 

 otherwise, and although he then, in 1894, intimated that signals 

 might be transmitted to a distance of half a mile by Hertzian 

 waves, it was not until Marconi began his memorable work that 

 really practical results were obtained. 



In the operation of his wireless telegraph system Marconi uses 

 an electric oscillator (figs. 4 and 5), the Branly coherer k, the Lodge 

 tapper /, in a local circuit, and the Poppott' vertical wire A, at 



the sending and receiving stations, all of 

 which devices, as has been shown, were 

 well known, and it has been by modify- 

 ing, improving, and perfecting these 

 devices, and by adding others, that 

 Marconi has been enabled to obtain his 

 excellent practical results. The im- 

 provements and additions that have, 

 perhaps, conduced more than anything 

 else to the first successful results ob- 

 tained by Marconi were those that re- 

 lated to the coherer and the vertical 

 wire. The sensitiveness of the coherer 

 he increased greatly by diminishing its size, compared with the Branly 

 coherer, and by employing a mixture of nickel filings and silver — 90 

 per cent of the former and 10 per cent of the latter metal. He 

 also placed the few filings used in a vacuum. The other instru- 

 ments, shown in fig. 5, are the relay, R, controlled by the 

 coherer, and an ink-recording instrument, E, controlled by 

 the relay. This figure illustrates the earlier arrangement of 

 Marconi's devices. In it the coherer is 

 directly connected with the lower end of 

 the vertical wire by one of its terminids 

 and with the earth by its other terminal. 

 In his later work, Marconi has dispensed 

 with the filings coherer, now employing 

 a magnetic detector, which is much more 

 sensitive than the coherer and does not 

 reciuire tapping. 



Beginning his experiments in Italy in 

 1S95 with vertical wires 20 feet in height, 

 Marconi foiuid that he could get signals 

 at a distance of 1 mile, and that by dou- 

 bling the height of the vertical wire at both stations signals could be 

 transmitted to four times that distance. Thus, with wires 40 feet 

 high he could signal 4 miles, and with wires 80 feet high, 1(3 miles. 



Fig. 5.— Outline of Marconi's earlier 

 devices. 



