198 Mr. G. Marconi [June 13, 



sounded by the violinist. Tuning-forks and violins, of course, have 

 to do with air waves and wireless telegraphy wth ether waves, but 

 the action in both cases is similar. It is very important to take into 

 consideration the one essential condition which must be obtained in 

 order that a well-marked tuning or electrical resonance may take 

 place. Electrical resonance, like mechanical resonance, essentially 

 depends upon the accumulated effect of a large number of small 

 impulses properly timed. Tuning can only be obtained if a sufficient 

 number of these timed electrical impulses reach the receiver. As 

 Prof. Fleming graphically puts it in one of his lectures on elec- 

 trical oscillations, to " set a pendulum in vibration by puffs of air 

 we must not only time the puffs properly, but keep on puffing for a 

 considerable period." It is, therefore, clear that a dead-beat radiator 

 — i.e. one that does not give a train or succession of electrical 

 oscillations — is not suitable for tuned or syntonic space telegraphy. 



As I pointed out before, a transmitter consisting of a vertical wire 

 discharging through a spark-gap is not a persistent oscillator. Its 

 electrical capacity is comparatively so small and its capability of 

 radiating waves so great that the oscillations which take place in it 

 must be considerably damped. In this case receivers or resonators 

 of a considerably different period or pitch will respond and be 

 affected by it. 



Early in 1900 I obtained very good results with another arrange- 

 ment in which the radiating and resonating conductors each take the 

 form of two concentric cylinders, the internal cylinder being earthed. 

 By using zinc cylinders only 7 metres high and 1 • 5 metres in diameter 

 good signals could easily be obtained between St. Catherine's Point, 

 Isle of Wight, and Poole, over a distance of 80 miles, these signals 

 not being interfered with or read by other wireless telegraph installa- 

 tions worked by my assistants or by the Admiralty in the immediate 

 vicinity. The capacity of the transmitter due to the internal con- 

 ductor is so large that the energy set in motion by the spark discharge 

 cannot all radiate in one or two oscillations, but forms a train of 

 slowly-damped oscillations, which is just what is required. A simple 

 vertical wire may be compared with an empty teapot, which, after 

 being heated, would cool very rapidly, and the concentric cylinder 

 system with the same teapot filled with hot water, which would take 

 a very much longer time to cool. In the receiver the closely adjacent 

 cylinders which give it large electrical capacity cause it to be a 

 resonator possessing a very decided period of its own, and it becomes 

 no longer apt to respond to frequencies which differ from its own par- 

 ticular period of electrical oscillation, nor to be interfered with by stray 

 ether waves which are sometimes caused by atmospheric disturbances, 

 and which occasionally prove troublesome during the summer. 



Another successful system of tuning or syntonising the apparatus 

 was the outcome of a series of experiments carried out with the dis- 

 charge of condenser or Ley den jar circuits. I tried by means of 

 associating with the radiating wire, or capacity, a condenser circuit, 



