1900.] on Wireless Telegraphy. 253 



vened, however great the distance attained, was apparently no obstacle 

 to the transmission. The maximum height of the top of the wire 

 attached to the instruments above the water did not on any occasion 

 exceed 170 feet, but it would have been geometrically necessary to 

 have had masts 700 feet high on each ship in order that a straight 

 line between their tops should clear the curved surface of the sea 

 when the ships were 60 nautical miles apart. This shows that the 

 Hertzian waves had either to go over or round the dome of water 

 530 feet higher than the tops of the masts, or to pass through it, 

 which latter course I believe would be impossible. 



Some time after the naval manoeuvres, with a view to showing 

 the feasibility of communicating over considerable distances on land, 

 it was decided to erect two stations, one at Chelmsford and another 

 at Harwich, the distance between them being 40 miles. These instal- 

 lations have been working regularly since last September, and my 

 experiments and improvements are continually being carried out at 

 Chelmsford, Harwich, Alum Bay, and North Haven, Poole. 



In the month of September last, during the meetings of the 

 British Association in Dover and of the Association Francaise pour 

 l'avancement de Science in Boulogne, a temporary installation was 

 fixed in the Dover Town Hall, in order that members present should 

 see the practical working of the system between England and France. 

 Messages were exchanged with ease between Wimereux, near Boulogne, 

 and Dover Town Hall. In this way it was possible for the members 

 of the two associations to converse across the Channel, over a dis- 

 tance of 30 miles. 



During Professor Fleming's lecture on the ' Centenary of the 

 Electric Current,' messages were transmitted direct to and received 

 from France, and via the South Foreland Lighthouse to the East 

 Goodwin Lightship. An interesting point was that it was demon- 

 strated that the great masses of the Castle Eock and South Foreland 

 cliffs lying between the Town Hall, Dover, and the lighthouse did 

 not in the least degree interfere with the transmission of signals. 

 The result was, however, by no means new. It only confirmed the 

 results of many previous exjieriments, all of them showing that rock 

 masses of very considerable size intervening between two stations do 

 not in the least affect the freedom of communication by ether wave 

 telegraphy. (See ' J ournal of the Institution of Electrical Engineer?," 

 April 1899, p. 280.) 



It was during these tests that it was found possible to communi- 

 cate direct from Wimereux to Harwich or Chelmsford, the intervening 

 distance being 85 miles. This result was published in a letter from 

 Professor Fleming addressed to the ' Electrician ' on September 29. 

 The distance from Wimereux to Harwich is approximately 85 miles, 

 and from Wimereux to Chelmsford also 85 miles, of which 30 miles 

 are over sea and 55 over land. The height of the poles at these 

 stations was 150 feet, but if it had been necessary for a line drawn 

 between the tops of the masts to clear the curvature of the earth they 



