January 7, 19 15] 



NATURE 



;oi 



reason the non-used lower harmonic frequencies 

 do not dissipate energ-y to such an extent as 

 greatly to lower the over-all efficiency of the 

 machine. Otherwise the book will prove to be a 

 useful text-book for class teaching for students 

 who come to the subject without much previous 

 knowledge. The book is well printed, and the 

 illustrations are well selected and drawn. The 

 diagram No. 54, representing the lines of electric 

 force round a Hertzian oscillator, is, however, not 

 very true to fact. The loops of force thrown off 

 should be concave on the inner side, and not 

 convex. 



(2) The book by Mr. Rolfe-Martin covers much 

 the same ground, but is marked by less originality 

 of illustration and more dependence on diagrams 

 borrowed from commercial publications or maga- 

 zines than is the case with Prof. Stanley's book. 

 It is also more occupied with descriptive matter 

 of the various appliances used by the Marconi 

 Company, the Telefunken Company, and others. 

 Nevertheless, it is well up-to-date, and for the 

 student who can afford to possess more than one 

 book on wireless telegraphy it is useful to have 

 illustrations of actual apparatus in various forms. 



Books which aim chiefly at an exposition of 

 first principles rather than ,at descriptions of 

 apparatus are likely to have more permanent value 

 because the principles remain, whereas types of 

 apparatus are being perpetually changed. In 

 both of the above-mentioned books the authors 

 have done wisely to discard all reference to early 

 and now antiquated forms of wireless telegraphy. 

 Neither of them, however, devotes much space to 

 the consideration of the problem of radio-tele- 

 phony. 



There is here a wide field yet open for inven- 

 tion. The invention of a simple, easily managed 

 generator of undamped waves and mode of modu- 

 lating their amplitude in accordance with the wave 

 form of the speaking voice offers a large scope for 

 invention, and one which, if successfully culti- 

 vated, may end in replacing radio-telegraphy by 

 radio-telephony to much the same extent as the 

 telephone has replaced the telegraph in the case 

 of wire transmission. 



It need scarcely be said that in books intended 

 for students there is no reference made in these 

 publications to the outstanding problems and 

 difficult questions of radio-telegraphy. The mode 

 of propagation of the waves over the earth's sur- 

 face is, however, dealt with by Prof. Stanley in his 

 tenth chapter in ' a manner sufficient to impart 

 some ideas of the nature of it as well • as of the 

 causes of the variations obser\-ed. It is becoming 

 more and more clear that our terrestrial atmo- 

 sphere plays an important part in long-distance 

 NO. 23i?8, VOL. Q4.1 



radio-telegraphy, and that if the earth were a good 

 conductor, say, as good as copper, and possessed 

 no atmosphere, anything like long-distance wire- 

 less telegraphy on it would probably be imposs- 

 ible. 



The progress of real knowledge on this subject 

 will therefore be to a large extent conditioned by 

 the progress of atmospheric meteorology- and a 

 knowledge of the state and constitution of the 

 upper air. J. A. F. 



TRANSLATIONS OF PO IN CARE ON 

 METHOD. 



(i) Science and Method. By Henri Poincar^. 

 Translated by Francis Maitland. With a Pre- 

 face by the Hon. Bertrand Russell. Pp. 288. 

 (London : Thomas Nelson and Sons, n.d.) 

 Price 65. net. 



(2) The Foundations of Science : Science and 

 Hypothesis; The Value of Science; Science 

 and Method. By H. Poincare. Authorised 

 translation by G. B. Halsted. With a special 

 Preface by Poincare, and an Introduction by 

 Josiah Royce, Harvard University. Pp. xi-f- 

 553. (New York : The Science Press, 1913.) 



(3) Wissenschaft und Methode. Von Henri 

 Poincare. Autorisierte deutsche Ausgabe mit 

 erlauternden Anmerkungen von F. und L. 

 Lindemann. Pp. vi + 283. (Leipzig und Ber- 

 lin : B. G. Teubner, 1914.) Price 5 marks. 



(4) Letzte Gedanken. Von Henri Poincare. 

 Mit einem Geleitwort von Wilhelm Ostwald. 

 Uebersetzt von Dr. Karl Lichtenecker. Pp. v — 

 261. (Leipzig : Akademische Verlagsgesell- 

 schaft, M.B.H., 1913.) Price 4.50 marks. 



DURING his lifetime Henri Poincare pub- 

 lished many articles on the philosophy of 

 science, and these were republished in three 

 books : "La Science et I'Hypoth^se," "La Valeur 

 de la Science," and "Science et Methode." After 

 his death, his " Derni^res Pensees " were collected 

 and published in 1913. Of the books under 

 review, (i) gives an English translation of the 

 third of Poincare's works just mentioned ; (2) 

 the first volume of a series on science and educa- 

 tion, gives an English translation of the first 

 three ; (3) gives a German translation of the third ; 

 and (4) gives a German translation of the post- 

 humous work. 



Poincare's lively style is verj' well reproduced 

 in (r), but in (2) the translation seems to aim 

 at the French spirit, and succeeds in giving an 

 almost comically literal rendering which is not 

 English and not even American. We will repro- 

 duce parallel passages of both books to show 



