1902.] upon the Propagation of Electromagnetic Impulses. 345 



brief description of the nature of the apparatus used at the transmit- 

 ting and receiving stations. 



The transmitter at Poldhu was similar in principle to that used by 

 me in previous work,* but the elevated conductor at the transmitting 

 station was much larger, and the potential to which it was charged at 

 the peak of each electrical oscillation very much in excess of any that 

 had been previously employed. The transmitting elevated conductor 

 consisted of fifty almost vertical naked copper wires, suspended at the 

 top by a horizontal wire stretched between two poles each 48 metres 

 high and placed 60 metres apart. 



These wires were separated from each other by a space of about 

 1 metre at the top, and, after converging together, were all connected 

 to the transmitting instruments at the bottom. The potential to 

 which these conductors were charged during transmission was sufficient 

 to cause sparking between the top of the said wires and an earthed 

 conductor across a space of 30 cm.f 



The general engineering arrangements of the electric-power station 

 erected at Poldhu for creating the electric waves of the frequency 

 which I desired to use, were made by Dr. J. A. Fleming, F.R.S., who 

 also devised many of the details of the appliances for producing and 

 controlling the electric oscillations. These, together with devices 

 introduced by me and my special system of syntonisation of inductive 

 circuits, have provided an electric-wave generating plant more power- 

 ful than any hitherto constructed. 



At the receiving station on the ship, one of my receivers, as described 

 in the Society of Arts paper above referred to, was employed, and 

 the signals were recorded on the tape of a Morse recording instru- 

 ment. 



A receiving transformer accurately tuned to the period of the 

 electrical oscillations radiated from the transmitting station at Poldhu 

 was connected to the coherer in the usual manner. 



The receiving elevated conductor was constituted of four almost 

 vertical wires sustained in position by the ship's mast, the summit of 

 which wires was about 60 metres above the sea-level. At their lower 

 end they were all connected to the receiving instrument. 



My assistants at Poldhu had received instructions to send a succession 

 of Ss and a short message at a certain pre-arranged speed, every ten 

 minutes, alternating with five minutes of rest, during the following 

 hours : — From 12 to 1 A.M., from 6 to 7 A.M., from 12 to 1 p.m., and 

 from 6 to 7 P.M-, Greenwich mean time, every day from the 23rd 



* See ' Journal of the Society of Arts,' vol. 29, pp. 506—517. 



t Note, added July 5, 1902. The spark-length here stated to be 30 cm. was, by 

 a misunderstanding on the part of the communicator of the paper, altered to 

 50 mm., which appeared on the first proof. It was correctly stated as 30 cnn in 

 the original MS. 



