NATURE 



239 



THURSDAY, AUGUST 24, 1911. 



TWO WORKS ON WIRELESS TELEGRAPHY. 



(1! Prdcis de Telegraphic sans Fil. Complement de 



I'Ouvrage : les Oscillations Electromagnitiques et 



la Telegraphie sans Fil, By Prof. J. Zenneck, 



Translated from the German by P. Blanchin, G. 



GueYard and E. Picot. Pp. x + 385. (Paris: 



Gauthier-Villars, 1911.) Price 12 francs. 



(2) A Handbook of Wireless Telegraphy : its Theory 



and Practice. Tor the Use of Electrical Engineers, 



Students, and Operators. By Dr. J. Erskine- 



Murruv. Third edition, revised and enlarged. Pp. 



xvi + 386. (London: Crosby, Lockvvood and Son, 



1911.) Price 10s. 6d. net. 



(1) ' I "HE literature of wireless telegraphy grows 



J- apace, both in new books and new editions. 



This at least is a proof that the art is in a progressive 



condition. The book by Dr. J. Zenneck before us 



is a French translation, under the title "Precis 



de Telegraphie sans Fil," of a work by him which 



appeared in Germany two years ago, called "Leitfaden 



der Drahtlosen Telegraphie." 



It is, as the author tells us, intended as a con- 

 densation and supplement of his larger treatise on 

 " Electrical Oscillations and Wireless Telegraphy," 

 published in 1905. In the present work mathe- 

 matical discussions have been almost completely 

 avoided, and the reader is referred to other sources for 

 the systematic proofs of the few formula; given. The 

 book appeals therefore to the general reader or prac- 

 tical worker who wishes for a non-mathematical but 

 scientific discussion of phenomena. The numerous 

 excellent diagrams, curves, arrangements of circuits, 

 and illustrations of apparatus are sufficient to convey 

 to the careful reader a large amount of solid informa- 

 tion on the subject. One good feature is that there 

 is no attempt to describe various " systems " of wire- 

 less telegraphv by different inventors; but the separate 

 elements which make up the arrangements generally 

 used are scientifically discussed. Beginning with the 

 analysis of the phenomena of oscillations in a con- 

 denser circuit and the measurement of the quantities 

 concerned, we have successive chapters on the trans- 

 formation of oscillations, resonance curves, antennae, 

 radiators, detectors, receiver circuits, and directive 

 telegraphy. 



The treatment for the most part follows orthodox 

 lines as adopted in other standard treatises on the 

 subject, and is characterised by a German thoroughness 

 of treatment, though marked by an occasional tend- 

 ency to claim for Germany rather more than is 

 Historically warrantable. Thus, for instance, the elec- 

 tric hot-wire thermometer figured on p. 66 is attri- 

 buted to Riess, whereas Sir William Snow Harris 

 first described it in the Philosophical Transactions of 

 the Royal Society in England in 1827, long before 

 Riess. In the same manner, Prof. F. Braun is given 

 credit on p. 161 for the modern coupled transmitter, 

 whether single coil or double coil, which is called 

 "l'^mitteur couple ou 6mitteur de Braun," although 

 NO. 2182, VOL. 87] 



the recent judgment- of Mr. Justice Parker in the 

 British High Court of Justice has declared that the 

 modern tuned coupled transmitter first described by 

 Marconi, whether used with a two coil or with an 

 autotransformer, was not anticipated by the inven- 

 tions of Braun. The double transformation trans- 

 mitter, the arrangement of which is figured on p. 173, 

 is 1 he invention of this reviewer, whose name, how- 

 ever, is not mentioned in connection with it. The 

 chapters on resonance curves and on antennae are 

 verv good, but that on transmitters might have been 

 improved by a little more attention to the description 

 and theory of impact dischargers, which are of con- 

 siderable importance. 



In discussing the action of directive antenna?, Dr. 

 Zenneck advances a theory — which is not, however, 

 supported in this book by mathematical proof — that 

 the explanatijn of the greater range of a bent antenna 

 in the direction opposite to that in which the free 

 end points is to be explained by the different shape 

 of the wave surface on the two sides, so that the 

 wave obtains a greater reach one way than the other, 

 just as a rifle when fired carries further if elevated 

 than if depressed. Another explanation has been 

 given by the writer, based on an opinion expressed by 

 Sir J. Larmor, that the bent antenna can be regarded 

 as a combination of closed and open antennae. This 

 theory receives experimental support from the work 

 of Bellini and Tosi on directive antennae. One of 

 the most interesting as well as practical questions 

 in connection with long-distance wireless telegraphy 

 is that of the atmospheric absorption and the influence 

 of daylight in reducing the range of transmission for 

 certain wave lengths. This is generally attributed to 

 ionisation of the atmosphere produced by ultra-violet 

 solar light. This solar radiation is, however, so 

 rapidly absorbed by the atmosphere that the chief 

 effect can only be produced at high altitudes. The 

 theory that it is due to the direct action of ultra- 

 violet light on the sending antenna is not supported 

 by any experimental evidence. The hypothesis that 

 it is due to ionisation of the air receives some con- 

 firmation from a certain variation of radiotelegraphic 

 range with variations in atmospheric electricity. It 

 is well known to radiotelegraphists that occasionally 

 atmospheric conditions exist in which quite extra- 

 ordinary and unusual distances are covered by day as 

 well as by night, and that curious differences exist in 

 the facility with which electric waves of large wave 

 length are propagated in different directions. 



We cannot say yet that the phenomenon has re- 

 ceived adequate explanation, but materials are being 

 slowly gathered which may in time point to an ex- 

 planation. The same may be said of the abnormal 

 manner in which electromagnetic waves of long wave 

 length travel round the curvature of the earth. Mar- 

 coni has succeeded in sending and detecting radio- 

 telegraphic waves at a distance of 6000 miles, or a 

 quarter of the way round the earth. The subject of 

 this abnormal diffraction has been discussed mathe- 

 matically by Poincare and by Nicholson, but the com- 

 plexity introduced by the purely atmospheric and sur- 



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