314 



NATURE 



[August i, 1895 



the appearance of the concluding volume of the treatise, 

 which will contain, inter iilia, a discussion of the 

 group of an equation, and of the classification of equa- 

 tions according to the nature of the groups belonging to 

 them. Until the work is complete, it is premature to 

 express an opinion as to the degree of success with which 

 the author has attained the object he has in view ; but 

 there can be no doubt of the valuable ser\'ice which is 

 rendered to science by the composition of a methodical 

 treatise like this. So far as we are able to judge, account 

 has been taken of all the most important researches 

 which come within the scope of the present volume ; the 

 three last sections, in particular, include an account 

 of the recently published papers of Helge von Koch, 

 Poincare, and Mittag-Lefller. 



The proof-sheets appear to have been ver>- carefully 

 revised, so that the book is happily free from the crowd of 

 misprints with which mathematical text-books, other\vise 

 excellent, are not unfrequently disfigured. G. B. M. 



////•. HESEARCHES OF TESLA. 

 Inventions, Researches, and Writings of Nikola Tesla. 

 By Thomas Commerford Martin. (New York : The 

 Electrical Engiiuer, 1894.) 



WE have here an account of Nikola Tesla, his 

 scientific inventions and work, by a devoted 

 admirer. Mr. Martin is not a Boswell, and from the 

 nature of the case his book could hardly have about it 

 all that human interest which pervades the life and 

 achievements of a veteran discoverer in science. Mr. 

 Tesla is a young man whose career has been somewhat 

 romantic, and whose ingenuity is such as to rank him 

 very high indeed among the electrical workers and dis- 

 coverers of the day. Born in .Austro-Hungary, educated 

 at the Rcalschule at Carstatt and the Polytechnic at 

 Gratz, and professionally first in the Government Tele- 

 graph Department, and afterwards in Paris, his career 

 as an engineer really began when he arrived in America 

 little more than ten years ago. 



In two or three years from the day on which he took 

 off his coat in the Edison Works, Tesla motors had 

 attracted attention, and he leaped at once to a position 

 as a successful experimenter and inventor, which his 

 subsequent work has only secured and made more im- 

 portant. His researches on the effects of alternating 

 currents of high potential and frequency, in particular, 

 though they had the misfortune to be made the subject 

 of the speculations of the ordinary journalist, are of great 

 scientific interest, and continued by Mr. Tesla himself 

 and the army of enthusiastic workers we now have, 

 cannot fail to yield theoretical results and practical 

 applications which will more than fulfil the anticipations 

 of ' ' ■! t<M)k a sober and rational view of their 



P" None of those who listened to Mr. Tesla 



at il Institution will soon forget the almost 



ni.' vpcriments performed, their clear exposition 



in what was to the lecturer manifestly a foreign language, 

 and the enthusiasm which the results displayed excited 

 in those present who were best able to judge of their 

 scientific interest and importance. 



Mr. Martin's account of .Mr. Tesla's work is interest- 

 ing, and ycl perhaps it might have been in some respects 

 NO. 1344, VOL. 52] 



better than it is. He has had excellent materials, such 

 as the various lectures delivered by Mr. Tesla on his 

 researches generally, the papers read from time to time 

 to scientific societies on particular inventions and points 

 of interest, and apparently the specifications of Mr. 

 Tesla's patents. Our complaint, if we have one, is that 

 this material has hardly been sufficiently worked up. 

 Many of the lectures and papers were, as was inevitable, 

 hurriedly composed, and the expression of Mr. Tesla's 

 theoretical \iews contained in them is not always so 

 clear and complete as it might have been made by one 

 not so rapidly carried forward by the stream of dis- 

 covery. .\ great inventor can hardly be expected to j 

 spend time weighing words and phrases, at any rate he > 

 has a title to be excused from doing so, which others 

 who expound him do not possess. As it is, Mr. Martin's 

 book is on the whole a reproduction of articles which 

 appeared from time to time in the Electrical Engineer 

 {ai New York), and all we wish is that he could have 

 spared the time and trouble necessary to cast the matter 

 into a more homogeneous and symmetrical form. 



For the lectures which are reproduced we are very 

 grateful. They give Mr. Tesla's own description of his 

 inventions, and his views on points of theory — views, 

 which if not always orthodox, and sometimes expressed 

 in language which appears strange, are ahvays fresh 

 and suggestive. The unavoidable repetitions of the 

 same ideas, and recurring descriptions of the same 

 apparatus, arc not without some advantage, though they 

 interfere with the unity of Mr. Martin's book, as they 

 enable the lecturer's meaning to be made out more com- 

 pletely than would otherwise be possible. 



The book is divided into four parts : Polyphase currents ; 

 Tesla effects with high frequency and high potential 

 currents ; miscellaneous inventions and writings ; early 

 phase motors and the Tesla oscillators. The two first 

 parts are of course much more interesting than the re- 

 maining two, which have to do with such things as oil 

 condensers, anti-sparking dynamo brushes, unipolar 

 generators, the Tesla exhibit at the World's Fair, and 

 the Tesla mechanical and electrical oscillators. 



The discussion of polyphase currents, which occupies 

 the first 1 1 5 pages of the book, has more unity of treat- 

 ment about it than the second part, which consists 

 mainly of the lectures Mr. Tesla delivered in this country 

 and .•\merica. After a short introductory and bio- 

 graphical chapter, Mr. Martin proceeds to expound the 

 principle of the rotating magnetic field and ihc con- 

 struction of synchronising motors. .X paper by Tcsl.i, on 

 a "New System of .Mtcrnatc Current Motors and Trans- 

 formers," is reproduced in this connection, and contains 

 the foundation on which is based the remaining twenty- 

 one chapters which make up Part i. These contain 

 numerous modifications of the original idea, man" of 

 them exceedingly ingenious. .A motor " dcpcndinj; on 

 'magnetic lag' or hysteresis" is described in Chapter xii. 

 The peculiarity of this is stated in an introductory para- 

 graph to be " that in il the attractive effects or phases, 

 while lagging behind the phases of current which produce 

 them, are manifested simultaneously and not succes- 

 sively." This statement itself seems to want some little 

 exposition, though the arrangement is really very simple. 

 .•\n iron disc is pivoted within a fixed coil, wound just 



