192 



SCIENCE. 



[N. S. Vol. YIII. No. 189. 



Continental writers on mechanics. They con- 

 sist in tlie use of antiquated if not ambiguous 

 terminology, like ' vitesse virtuelle,' ' quantite 

 de mouvement,' ' force vive,' etc.; and in the 

 treatment of mass as a mere mathematical in- 

 convenience to be got out of sight, if not out of 

 mind, as soon as possible. 



As may be inferred from the three volumes 

 aggregating upwards of 900 pages, there is room 

 in the work of Professor Du Bois for pretty 

 thorough treatment of the elements of mechan- 

 ics. A detailed examination of the work will 

 convince one that this room has been well 

 filled. Many parts of the work might have 

 been much condensed and some parts might 

 have been omitted entirely without detri- 

 ment to an elementary book, but it was the 

 purpose of the author to prepare a text-book 

 which would be of use to students during the 

 whole of their college course and afterwards 

 as a work of reference. This purpose, it must 

 be said, has been very well executed, and the 

 work will prove exceedingly useful to teachers 

 and professienal readers as well as to students. 



The plan of the work is in accordance with 

 the divisions of the science adopted by Thom- 

 son and Tait in the Natural Philosophy ; the 

 first part being devoted to kinematics, and the 

 last two to dynamics, that is, to statics and 

 kinetics respectively. The development of the 

 fundamental principles is systematic and log- 

 ical, and an invaluable feature of the volumes is 

 found in the large number of numerical ex- 

 amples fully worked out. By means of typo- 

 graphical devices the author appeals to all 

 classes of readers, the paragraphs in large type 

 forming an abridged course, the articles in 

 small type being for advanced students, and 

 articles involving the use of the calculus being 

 set off by brackets. Italics and full-face type 

 are also used with a freedom which seems 

 Teutonic rather than English in its tendencies, 

 and many readers will wonder how statements 

 which are already admirably clear and intelligi- 

 ble are rendered more so by those pictorial de- 

 vices. 



The volumes devoted to kinematics and 

 statics are very full of well arranged and di- 

 gested matter for an elementary work, the vol- 

 ume on statics containing also four chapters 



(158 pp.) on retaining walls, elasticity of ma- 

 terials, theory of flexure and the continuous 

 girder, respectively. The volume on kinetics is 

 likewise quite complete, all but one short chap- 

 ter on the gravitational potential being occupied 

 with what may be called pure theory. 



Amongst many commendable features of the 

 work of Professor DuBois special mention should 

 be made of the clearness of definition and the 

 precision of terminology which prevail through- 

 out the volumes. In these respects the work is 

 on the whole especially satisfactory. The only 

 exceptions we have noted are in Chapter VIII. 

 of Vol. III. , wherein the potential as defined by 

 equation (1) does not appear to have the dimen- 

 sions assigned to it in problem (11). In the 

 same chapter also, p. 113, a well known theorem 

 of Gauss is attributed to Laplace ; while on pp. 

 114 and 115 Poisson's extension of Laplace's 

 theorem is referred to without explanation of 

 Laplace's theorem itself. 



Professional and unprofessional students who 

 have read Professor Tait's profound article on 

 mechanics in the last edition of the Encyclopse- 

 dia Britannica welcome the reprint of that arti- 

 cle with additions in the handy text-book form 

 presented by the Messrs. Black. Some modi- 

 fications of the original article have been made 

 in this reprint, and the subjects of attractions, 

 hydrostatics, hydrokinetics and waves have 

 been incorporated as additions. The result is 

 a treatise on dynamics which for thought-pro- 

 moting information per unit area is equalled 

 only by the Natural Philosophy of Thomson and 

 Tait. Every student will feel a regret that the 

 author did not enlarge the work much beyond 

 its present limits. This regret is especially 

 keen with respect to Chapter V., wherein the 

 methods of Lagrange and Hamilton are all too 

 briefly developed. But the author anticipated 

 and answered this criticism. In his preface he 

 says : " One obvious objection may be made to 

 many parts of this book — undue brevity. It 

 was inevitable, when much had to be com- 

 pressed into moderate space ; yet, at the worst, 

 is not brevity, if it but convey its message, 

 transcendentally preferable to prolixity?" 



The work of Professor Wright is a completely 

 rewritten edition of his book on mechanics pub- 

 lished a few years ago. A larger page and 



