Notices respecting New Books. 173 



his age. "With his retirement M. W^olf's first volume ends : we 

 shall look forward with interest to the appearance of the second, 

 and its proposed account of the subsequent developments of the 

 Paris Observatory, particularly under Le Terrier, whose directorship 

 (during which the writer of this notice paid his only visit to 

 the establishment) was interrupted and resumed after the death 

 of Delaunay. Two directors, Arago and Mouchez, were natives 

 of Spain. The present eminent head of the Paris Observatory 

 M. Loewy, is a Viennese, and was invited to Paris by Le Verrier ; 

 he is also editor of the Connaissance cles Temps. Astonishment 

 has sometimes been expressed that Picard, its founder, was not, 

 instead of Cassini, appointed the first director of the Paris 

 Observatory, but M. Wolf gives reasons why the former preferred 

 the arrangement actually made. The work is illustrated, and 

 has for a frontispiece a representation of a visit by Louis XIV. to 

 the Observatory. W. T. Lynn. 



An Elementary Treatise on Alternating Currents. By "W. G„ 



Rhodes, 3I.Sc. Pp. xii + 212. London: Longmans, Green & Co. 



1902. 

 The literature of alternating currents is growing apace, and the 

 next few years will probably witness a considerable number of 

 additions to the text-books on this highly important subject. Since 

 the recognition of the fact that alternating currents offer the only 

 satisfactory solution of the problem of power transmission over 

 very long distances, engineers have taken a keen interest in this 

 branch of applied science, and the demand for suitable text-books 

 appears to have been considerable. 



The book before us is evidently intended for readers possessing a 

 fair knowledge of elementary mathematics, including the elements 

 of differentiation and integration, and should prove especially 

 useful to students in technical colleges. We fully share the author's 

 view that the elements of vector algebra should form part of the 

 curriculum of every technical school. 



In the first eight chapters, which contain a brief account of 

 alternating-current theory, the author is at his best. The numerical 

 examples given at the end of each chapter should prove of great,, 

 assistance to the student. Chapter IX, calls for some criticism. 

 In dealing with a Fourier series, most modern writers agree in 

 calling the " fundamental " the first harmonic term, its " octave " 

 the second harmonic, and so on (this, for instance, is the method 

 adopted by J. J. Thomson and Poynting in their text-book on 

 Sound). The author begins by adopting the old and now generally 

 abandoned method of regarding the first term as the fundamental, 

 and calling the remaining terms the 1st, 2nd, &c. harmonics. 

 Immediately afterwards, however, he states (p. 67) that " even 

 harmonics are generally absent from the curves representing 

 alternating currents "' — when it is clear that he means odd har- 

 monics, if his own nomenclature be adopted. This point is likely 

 to occasion considerable confusion in the mind of the student. 



The account of methods of testing transformers given in 



