6oo 



NATURE 



[June 29, 191 1 



radio-telegravhy: 



'T'HE practical upplicntion of electric waves to the pur- 

 ^ poses of wireless telegraphic transmission over long 

 distances has continued to extend to a remarkable degree 

 during the last few years, and many of the difficulties 

 which at the outset appeared almost insurmountable have 

 been gradually overcome — chiefly through the improved 

 knowledge which we have obtained in regard to the sub- 

 ject generally and to the principles involved. 



The experiments which I have been fortunate enough 

 to be able to carry out on a much larger scale than can 

 be done in ordinary laboratories have made possible the 

 investigation of phenomena often novel and certainly 

 unexpected. 



Although we have — or believe we have — all the data 

 necessary for the satisfactory production and reception of 

 electric waves, we are yet far from possessing any very 

 exact knowledge concerning the conditions governing the 

 transmission of these waves through space, especially over 

 what may be termed long distances. Although it is now 

 perfectly easy to design, construct, and operate stations 

 capable of satisfactory commercial working over distances 

 up to 2500 miles, no really clear explanation has yet been 

 given of many absolutely authenticated facts concerning 

 these waves. .Some of these hitherto apparent anomalies 

 I shall mention briefly in passing. 



Why is it that when using short waves the distances 

 covered at night are usually enormously greater than those 

 traversed in the daytime, whilst when using much longer 



V 



^□^ 



--Y ■- 





Fig. I 



Fic. 



waves the range' of transmission by day and night is 

 about equal, and sometimes even greater by day? 



What explanation has been given of the fact that the 

 night distances obtainable in a north-southerly direction 

 are so much greater than those which can be "effected in 

 an east-westerly one? 



Why is it that mountains and land generally should 

 greatly obstruct the propagation of short waves when sun- 

 light is present, and not during the hours of darkness? 



The general principles on which practical radio-tele- 

 graphy is based are now so well known that I need only 

 refer to them in the briefest possible manner. 



Wireless telegraphy, which was made possible by the 

 fields of research thrown open by the work of Faradav, 

 Maxwell, and Hertz, is operated by electric waves which 

 are created bv alternating currents of very high frequency 

 induced in suitably placed elevated wires or capacitv areas. 

 These waves are received or picked up at a distant station 

 on other elevated conductors tuned to the period of the 

 waves, and the latter are revealed to our senses by means 

 of appropriate detectors. 



My original system as used in 1896 consisted of the 

 arrangement shown diagrammatically in Fig. i, where 

 an elevated or vertical wire was employed. This wire 

 sometimes terminated in a capacitv, or was connected to 

 earth through a spark gap. 



1 Discourse delivered at the Royal Iirititution on Friday, June 2, by 

 Commendatore G. Marconi. 



NO. 2174, VOL. 86] 



Fig. 



By using an induction coil or other source of sufficiently 

 high-tension electricity, sparks were made to jump across 

 the gap ; this gave rise to oscillations of high frequency 

 in the elevated conductor and earth, with the result that 

 energy in the form of electric waves was radiated through 

 space. 



\x the receiving station (Fig. 2) these waves induced 

 oscillatory currents in a conductor containing a detector, 

 in the form of a coherer, which was usually placed 

 between the elevated con- 

 ductor and earth. 



.Although this arrange- 

 ment was extraordinarily 

 efficient in regard to the 

 radiation of electrical 

 energy, it had numerous 

 drawbacks. 



The electrical capacity of 

 the system was very small, 

 with the result that the 

 small amount of energy in 

 the aerial was thrown into 

 space in an exceedingly 

 short period of time. In 

 other words the energy, 

 instead of giving rise to a 

 train of waves, was all dis- 

 sipated after only a few 

 oscillations, and, conse- 

 quently, anything approach- 

 ing good tuning between 

 the transmitter and receiver 

 was found to be unobtainable in practice. 



Many mechanical analogies could be quoted which 

 show that in order to obtain syntony the operating energy 

 must be supplied in the form of a sufficient number of 

 small oscillations or impulses properly timed, .\coustics 

 furnish us with numerous examples of this fact, such as 

 the resonance produced by the well-known tuning-fork 

 experiment. 



Other illustrations of this principle may be given, e.g. 

 if we have to set a heavy pendulum in motion by means 

 of small thrusts or 

 impulses, the latter • 

 must be timed to the 

 period of the pendu- 

 lum, as otherwise its 

 oscillations would 

 not acquire any 

 appreciable ampli- 



tude. 



In 1900 I first 

 adopted the arrange- 

 ment which is now 

 in general use, and 

 which consists (as 

 shown in Fig. 3) of 

 the inductive associa- 

 tion of the elevated 

 radiating wire with 

 a condenser circuit, 

 which may be u.sed 

 to store up a con- 

 siderable amount of 

 electrical energy and 

 impart it at a slow 

 rate to the radiating 

 wire. 



As is now well 

 known, the oscilla- 

 tions in a condenser F""- 4- 

 circuit can be made 



to persist for what is, electrically, a long period of 

 time, and it can be arranged, moreover, that by means of 

 suitable aerials or antenna; these oscillations are radiated 

 into space in the form of a series of waves, which through 

 their cumulative effect are eminently suitable for enabling 

 good tuning or syntony to be obtained between the trans- 

 mitter and receiver. 



The circuits, consisting of the condenser circuit and the 

 elevated aerial or radiating circuit, were more or less 

 closely coupled to each other. By adjusting the inductance 



