130 



NA rURE 



[June 6, 1901 



for this reason we think Italian men of science are well ad- 

 vised to insist upon the recognition of the services of their 

 famous countryman, and they may be assured that all 

 who value solid work diligently performed will give a 

 grateful thought to the unostentatious astronomer of 

 Palermo, who devoted himself with skill and patience to 

 the laborious, and perhaps unappreciated, work of 

 cataloguing the stars. W. E. P. 



M 



SYNTONIC WIRELESS TELEGRAPHY. 

 R. MARCONI'S lecture on "Syntonic Wireless 

 Telegraphy," recently delivered before the Society 

 of Arts, gives an admirable and most interesting descrip- 

 tion of the system which he has developed and of the 

 steps by which the development has been effected. " I 

 have come to the conclusion," said Mr. Marconi, " that 



"^77777, 



the days of the non-tuned system are numbered." If 

 this prophecy be correct the non-tuned system has had, as 

 was indeed expected, but a short life ; but even in the 

 few years that it has been in use it has accomplished 

 much, having already to a certain extent greatly increased 

 the pleasure and, above all, the safety of travelling by sea. 

 There can be no better evidence of the general utility of 

 wireless telegraphy than that the time has already arrived 

 when the imperfections of the untuned system are making 

 themselves felt. To quote Mr. .Marconi again, " The 

 ether about the English Channel has become exceed- 

 ingly lively, and a non-tuned receiver keeps picking up 

 messages from various sources which very often render 

 unreadable the message one is trying to receive." 

 That this confusion of messages would sooner or later 

 occur many prophesied in the early days of the art, but 

 few, we think, seriously believed that it would come about 

 so soon. Fortunately, now that the evil is beginning to 



NO. 1649, VOL. 64] 



be felt, Mr. Marconi is ready with the remedy, a well- 

 worked-out and trustworthy system of tuned transmitters 

 and receivers. 



The original form of Mr. Marconi's transmitting 

 arrangement is too well known to need illustration : it 

 consisted of an induction coil the secondary terminals 

 of which were connected to a spark gap between two 

 brass balls, one of these being earthed and the other con- 

 nected to a long aerial conductor. Such a transmitter 

 has a very low electrical capacity, and its radiating power 

 is comparatively great. As a result, the oscillations 

 which take place are considerably damped, and all the 

 energy is radiated in one or two strong swings. Any 

 receiving apparatus in the neighbourhood which is suffi- 

 ciently sensitive will respond to these radiations even 

 although its natural time of vibration differs greatly from 

 that of the transmitter. Selection of messages with this 

 arrangement is possible, to a limited extent, by using 

 aerial conductors of considerably different lengths and 



I 

 I 

 I 



by winding the induction coils on the receiving appa- 

 ratus with the length of wire necessary for correct 

 resonance. But although this answers when the two or 

 more transmitting stations are at different distances from 

 the receiving station, it has been found not to work satis- 

 factorily when the distances are equal. 



It is necessary, therefore, to employ some form of 

 radiator in which the oscillations are less damped and 

 which will therefore emit a train of waves instead of one 

 or two strong vibrations. These feebler impulses, falling 

 in succession upon a receiver having the same time of 

 vibration, will get up a swing sufficiently strong to break 

 down the high resistance of the coherer. If, however, 

 the receiver is not in tune, the impulses will not tend to 

 get up any swing, and, being individually too feeble to 

 break down the coherer's resistance, no signal will be 

 recorded. Such a radiator can be constructed as shown 

 in Fig. I, in which the aerial conductor takes the form 

 of two concentric cylinders, the inner, a', being connected 

 to earth and to one side of the spark gap, and the outer, 



