28 



NA TURE 



'yNov. 12, 1885 



OUR BOOK SHELF 



Elementary Mechanics. By O. J. Lodge. (London and 

 Edinburgh: Chambers, 18S5.) 



This is a revised edition of Prof. Lodge's Text-Book : — 

 not much altered, so far as we can see even by the help 

 of the rapid yet searching stereoscopic squinting, from 

 the former edition. Why a writer, who begins by 

 acknowledging his indebtedness to the really scientific 

 works of Thomson andTait, Clerk-Maxwell, and Clifford, 

 should make frequent references to the merely " popular" 

 and singularly loose brocluires of Deschanel and Ganot, 

 is a question more easily asked than answered. But it is 

 totally unintelligible to us that, having begun with 

 classical works, he should proceed to " recommend real 

 students to read one or other " of theie poor compilations. 

 Was it not Horace Smith who said : — 



" Is there such scanty store of standard works, 

 That students must be fed on foreign trash ? " 

 But Prof. Lodge's own standard is far above that of the 

 books to which he, unfortunately and unaccountably, 

 refers his "real students." His work is a curious one. 

 There is scarcely a trace of the dogmatism which is 

 asserted to be so natural to the genus Professor ! The 

 author seems to place himself on the same level with his 

 reader, and anxiously to seek for confirmation of his own 

 statements in the assent of his pupils. This is, to say the 

 least, unusual ; but we cannot at once either commend, 

 or find fault with, it. It is a new departure, and its value 

 and usefulness must be judged by its success. 



There are a few elementary, but important, points in 

 Dynamics, by his treatment of which every author on the 

 subject shows at once whether he is " sound in the faith " 

 or not. On the whole. Prof Lodge passes these tests 

 with credit ; and the rest of his book is of a much higher 

 order than the run of elementary treatises. 



There are, however, here and there some singular slips, 

 which should be corrected in future editions. We note 

 only one or two, but even these are destructive of the 

 character for definiteness and accuracy which should be 

 the leading feature of every scientific book. Thus, in 

 §5 (where, unfortunately, a " statical " definition of force is 

 introduced as well as a " kinetic " one) we are told that 

 change of mo/ion. "is called" Acceleration : though in 

 later sections the true meaning : — i.e. Rate of Change of 

 Velocity : — is assigned to Acceleration. To the mere 

 popular reader this may appear hypercriticism ; but 

 science is most careful to distinguish not only between 

 Change and Rate of Change, but also between Motion 

 and Velocity. Again, in § 16, serious confusion is intro- 

 duced by the statement that the velocity of a point at 

 unit distance from an axis "is called" the angular velo- 

 city of the rotating body. Prof Lodge knows perfectly 

 well that it is not so, and that none but unscientific people 

 could confound a quantity of dimensions [T"i] with an- 

 other of dimensions [LT"'] ; even when, as in the present 

 case, their nutncrical values happen to be equal. We are 

 tempted to seek an explanation of, and thus to find an 

 excuse for, these andother similar slips, in his inexcusable 

 partiality for the works of Deschanel and Ganot. 



P. G. T. 



The Ocean, &c. By W. L. Jordan. .Second Edition. 

 (London: Longmans, 1S85.) 



Of this elaborate work it is enough to say that it is based 

 on " The .New Principles of Natural Philosophy." These 

 principles \ye sketched (June 21, 18S3) in an article 

 which, as his mode of ac nowledgment showed, was by 

 no means satisfactory to our .Author. That Vis Ine>-tice 

 was entirely misunderstood by Newton, and that ten- 

 resisted motion ultimately comes to rest, are among the 

 chief foundations of this work ! That a terrestrial globe 

 whose frame is carried round through a portion of a 

 curve, and then suddenly stopped, will rotate in conse- 



quence, is conceivable : but we should try to explain the 

 fact by bad centering, or some such cause : certainly not 

 by the assumption that, during the curvilinear motion, 

 one part of the equator had necessarily a greater linear 

 velocity than the opposite part. Our Author does not 

 seem to be acquainted with the most elementary properties 

 of the kind of motion called Translation ! But this is 

 merely, on his part, the most recent revival of Jelinger 

 Symonsism : — for it assumes the fundamental tenet of 

 that peculiar heresy ; viz. that a body, which revolves 

 round a centre, is not rotating if it turn always the same 

 side to the centre. It is needless to say more on this 

 melancholy waste of time, trouble, and ready money (the 

 latter especially) : on the part of an author who has been 

 complimented by a reviewer of one of his other works as 

 having " a familiar acquaintance with questions of 

 finance." See Advertisement appended to the present 

 volume. P. G. T. 



Spectrum Analysis. By Dr. H. Schellen. Translated 

 from the Third German Edition by Jane and Caroline 

 Lassell. Edited, with Notes, by Capt. Abney, R.E., 

 F.R.S. (London: Longmans, 1885.) 

 This is the second editiin rf a well known book: in its 

 general arrangement the. : is little departure from the 

 first, which appeared in 1872. While the German edition 

 from which it has been translated was being prepared, 

 the author unfortunately died ; it is not to be wondered 

 at therefore that the present reprint does not reflect the 

 present state of our knowledge so accurately as did the 

 former one ; indeed there is evidence that the German 

 editor has been compelled by the sad circumstances under 

 which this task devolved upon him to take what was 

 readiest to his hand. 



Some of the material however is very valuable : thus, 

 for instance, we have a complete and well illustrated 

 account of Vogel and Huggins' work on the spectra of 

 stars, much interesting information concerning Prof 

 Rowland's new concave gratings ; while the English 

 editor has added a full account of Abney, Festing, and 

 Langley's work on infra-red spectra, and Abney and 

 Schuster's discussion on the photographs taken during 

 the eclipse of 1882. With these exceptions the English, 

 French, or Italian work accomplished during the last ten 

 years is but imperfectly referred to. The names of 

 Thollon and Tacchini, to say nothing of Crookes and 

 Hartley, not even being in the index. To the student 

 therefore the book is worse than useless, it is misleading. 

 The popular reader, however, who does not care too 

 much for completeness will find much information con- 

 veyed in a pleasant form. The main branches of the 

 science, both in its terrestrial and celestial applications, 

 are dealt with, and the methods of work are given. Great 

 interest also attaches to the various forms of instru- 

 ments used in the new science ; many of these are 

 described, from a new form of pocket spectroscope — 

 which we learn from the index was devised by Capt. 

 Abney — to the more complex apparatus designed by 

 Vogel, von Konkoly, and others. 



The theoretical parts are perhaps most to be avoided. 

 The chapter on the plurality of spectra, for instance, 

 will help the reader very little in coming to a conclusion 

 upon a subject of fundamental importance. Such a state- 

 ment, too, as that on p. 268, " That Kirchhoff's theory 

 has received full confirmation from the observations of 

 solar total eclipses" is not so true as the writer evidently 

 thought it to be. 



Again, on the question of the change of refrangibiliiy 

 of light due to the motion of a light source towards or 

 from the eye. The complete statement made by Fizeau 

 in 1848 appears to be unknown to the author, who attri- 

 butes the solution of the problem to Mach, of Prague, in 

 the year i860. 



The translators have done their work throughout in a 



