NA TURE 



497 



THURSDAY, SEPTEMBER 19, 1901. 



WIRELESS TELEGRAPHY. 

 Dralttlosc Telegraphic diirch Wasser imd Lit//. Based 

 on Lectures delivered in the Winter of 1900 by Prof. 

 Dr. Ferdinand Braun, Director of the Physical Institute 

 of the University of Strassburg. Pp. 68. (Leipzig : 

 Veit and Co., 1901.) Price M. 2. 



THE rapid development of wireless telegraphy which 

 has taken place in the last few years has called 

 forth many articles in the scientific and technical papers, 

 but as yet but few single treatises or text-books. Prof 

 Braun is known as an experimenter in this branch of 

 electrical science, and the pamphlet under notice treats 

 of the subject from a more or less popular point of view 

 and also gives a short sketch of some of Prof. Braun's 

 own experiments. The first chapter is an interesting 

 historical resume of the endeavours to signal over a dis- 

 tance without the use of intervening wires. It is inter- 

 esting to observe that the discovery that the earth could 

 serve as a return conductor for the ordinary telegraph 

 first led up to the thought that the other wire could also 

 be replaced by the earth or air or other medium. In one 

 point we think Prof. Braun's remarks are hardly in 

 agreement with the latest of our ideas — we mean in his 

 description of the Becquerel and radium rays as being of 

 the nature of light and electric waves. This is hardly in 

 accordance with the corpuscle theory, which approaches, 

 as near as it is possible at present, to an explanation of 

 these phenomena. The chapter after this historical intro- 

 duction deals with the author's own experiments on 

 hydrotelegraphy. The guiding idea of the work was to 

 use the property of an alternating current, with sufficiently 

 high frequency, to flow only on the surface of a conductor. 

 If, now, such a current be led in and out at two points of 

 a sheet of water, the current, instead of penetrating deep 

 down, will tend to spread itself out upon the surface of the 

 water, and by connecting a receiving circuit at any two 

 other points, messages can be passed between the two 

 stations. This method of working differs in principle 

 from that of Rathenau and Strecker, who used stationary 

 currents. With this arrangement, if the receiver be con- 

 nected to two points lying on an equipotential line, i.e. a 

 line drawn at right angles to the current lines, no messages 

 can be received. With Braun's arrangement this is 

 different, due to the fact that the equipotential lines con- 

 tinually change. With experiments made at Cuxhaven, 

 signals could be sent for a distance of three kilojnetres, 

 it being proved tTiat the effect was neither transmitted 

 through the air nor was it an induction effect similar 

 to Preece's experiments. All the results agree fully with 

 the enunciated principle. 



It is difficult, however, to think, in spite of the author's 

 hopes, that this system will ever be of much practical 

 importance in view of the development of the Marconi 

 system. 



The second chapter gives an account of Prof. Braun's 

 experiments on wireless telegraphy proper. The results 

 of these experiments have been published in various 

 papers and have also received attention in this Journal. 

 The transmitter arrangement mostly used by Braun is 

 NO. 1664, VOL. 64] 



that of inductive excitement. Tested against the 

 Marconi arrangement, much better results were obtained, 

 and Prof. Braun is of opinion that this is the best of all 

 the devised arrangements up to date. It must be 

 remembered, however, that Marconi has considerably 

 improved his apparatus quite recently and has now 

 obtained results better than those given here. 



The next chapter is on "tuned telegraphy"; it is 

 pointed out that an un- or very little damped vibration 

 is the first condition for good syntony. This principle is 

 now universally recognised. 



In his final remarks. Prof. Braun is of opinion that the 

 hopes that have been entertained that wireless telegraphy 

 will ever displace the ordinary wire telegraphy are an 

 illusion, a conclusion which is now becoming general. 

 The spheres of usefulness of wireless telegraphy are, 

 however, even without this, very great, and in the near 

 future will greatly develop. 



As a short, clearly written contribution to the literature 

 of the subject, the book is worth reading. C. C. G. 



OUR BOOK SHELF. 



Geometrical Exercises from Ni.von's " Euclid Revised" 

 with Solutiotis. By Alexander Larmor, M.A. Pp. 

 vi -f 170. (Oxford : Clarendon Press, 1901.) 

 This is a collection of 823 examples illustrating the 

 various propositions of Euclid's six books, as well as 

 many other domains of the geometry of the right line and 

 circle, such as maxima and minima, collinearity and con- 

 currency, centres of similitude, coaxal circles, inversion, 

 harmonic ranges, poles and polars, and the modern 

 geometry of the triangle. It will thus be seen that every- 

 thing of importance in the subject is dealt with. Hints 

 are given for the solution of all the more easy questions, 

 while fully worked out solutions are given for the more 

 advanced. The work is therefore one of very great value 

 both for the student and for the teacher. All the classical 

 problems and theorems in the subject are associated with 

 the names of their discoverers — Ptolemy, Euler, Pascal, 

 Brianchon, Simson, &c. — and each receives ample illus- 

 tration and application. This is one of the many good 

 features of the work. Mr, Larmor is quite right in main- 

 taining that the student of geometry should be provided 

 with a copious and varied collection of exercises, and 

 with an opportunity for consulting the solution of a prob- 

 lem or theoi'em in which he has failed while his interest 

 in it is still fresh. Such an opportunity is afforded by 

 this excellent representative collection. Doubtless much 

 assistance in this way is derivable from the work of the 

 late Prof. Townsend ; but his book is, perhaps, too 

 elaborate and unmanageable for the average student, on 

 whose attention many other branches of mathematics 

 now make large demands. 



Histoire du Ciel. Par Clemence Royer. Pp. 246. 

 (Paris: Librairie C. Reinwald, 1901). Price 2 fcs. 50. 

 While correctly stating a considerable number of facts, 

 this little book, which forms the first volume of a " Petite 

 Encyclopedie Scientifique du XX' Si^cle," by no means 

 represents the state of astronomical science at the present 

 time. The earlier chapters recount the history of astronomy 

 to the time of Newton, but afterwards the bulk of the 

 matter is descriptive and speculative. So little acquainted 

 is the author with recent work, that among many strange 

 ideas expounded we find the suggestion that the rings of 

 Saturn are not composed of multitudes of small bodies 

 but of coherent masses of ice. The illustrations are very 

 poor, and the book should be avoided by those desiring a 

 trustworthy guide to current opinions. 



Y 



