June 15, 1882] 



NATURE 



149 



63 may have been originally drawn by M. Bertrand ; 

 but, as no reference is given, we cannot meantime 

 be sure whether his claim is any better than that of 

 Clausius. 



Detailed analysis being clearly out of place here, we 

 conclude with a few running comments on the different 

 parts of the work. The first part deals with Electro- 

 statical Phenomena. Except that we think the introduc- 

 tory chapter somewhat hurried and meagre, we commend 

 the general simplicity of the arrangement. A quasi- 

 physical proof of most of the general propositions con- 

 cerning electrified systems is given, and, we think, in the 

 interest of the physical reader, that this is right. The 

 seventh chapter of this part is especially recommended to 

 the notice of our readers ; there, so far as we know for 

 the first time, Sir W. Thomson's theory of dielectrics 

 finds its place in a text-book on Electrostatics ; both here 

 and in the corresponding chapters on Magnetism the 

 authors show a complete appreciation and mastery of this 

 important step in mathematical physics. Until Maxwell's 

 treatise was written, this piece of Thomson's work had 

 been apparently forgotten. It has lately been taken up 

 in Germany, more especially by Helmholtz more sno. 

 This neglect is no doubt to be explained by the equal 

 neglect of the ideas of Faraday, of which Thomson's 

 theory is the mathematical embodiment. The errors one 

 occasionally finds on this subject in continental text- 

 books of authority are very surprising, e.g. it will be 

 found stated that a small sphere of magnetic or dia- 

 magnetic substance tends to move along the lines of 

 force j the better diffusion of the true theory will surely 

 tend to prevent such fundamental mistakes as this. 

 The application of Thomson's theory to dielectrics is 

 most interesting and important theoretically ; but great 

 difficulty has been found in verifying it experimentally, 

 owing to the scarcity of bodies that will insulate suffi- 

 ciently well. Its application to magnetics has been most 

 successful, as our readers doubtless know. 



The second part treats of electric currents, stationary 

 and variable, and will probabiy be found well suited for 

 the higher class of practical electricians ; the account of 

 the theory of telegraphic signalling deserves special 

 mention. In Chapter II. of this part the authors are 

 more cautious as to Volta's law of contact than they are 

 at the end of the former part, knowing doubtless, as 

 sound practicians, that they are on delicate ground. 



The theory of magnetism, which constitutes the third 

 part, suffers, as did the electrostatics, in the .beginning, 

 from the suppression of experimental detail. We cannot 

 reconcile ourselves to the definition given of the magnetic 

 axis as the line joining the poles of the magnet. This 

 seems a very artificial and difficult way of introducing this 

 fundamental conception ; and we do not see the advan- 

 tage over the ordinary method, which defines it as that 

 direction which is always found parallel to a certain fixed 

 vertical plane when the magnet is suspended freely under 

 the earth's action alone at a given time and place. We 

 also fail to see why, in mentioning the hypotheses ad- 

 vanced to explain terrestrial magnetism, Gilbert and Biot 

 should be mentioned, and Halley and Hansteen forgotten. 

 In other respects, this part of the work gives as good an 

 account of its subject as most treatises we have seen. 

 Our readers may note the discussion of the direct mag- 



netic action of the heavenly bodies as something fresh in 

 a text-book. 



The last part of the work deals with Electro-magnetism. 

 The connection between a current and the equivalent 

 magnetic shell is deduced in a very ingenious (although 

 we scarcely think simple) way from the law of Biot and 

 Savart. The other method, which we prefer, is also 

 given, in which the elementary proposition is that a plane 

 circuit, whose linear dimensions are infinitely small com- 

 pared with the distance of the point at which its action is 

 considered may be replaced by a small magnet. A sepa- 

 rate chapter is very properly given to the Methods of 

 Ampere, and the authors have shown their judgment in 

 refraining from loading their pages with the various solu- 

 tions of the indeterminate problem to find the elementary 

 law of electrodynamic action ot which we have lately had 

 a superfluity. An excellent account is given of the general 

 theory of Maxwell. The only thing we would take objection 

 to is yet another meaning given to that overburdened 

 word Electromotive Force; the authors use Force Electro- 

 mot rice Tot ale in place of Maxwell's Vector Potential. 

 The deduction of the rotation of the plane of polarisation 

 from Hall's phenomenon is given ; but Prof. Rowland's 

 name is not mentioned in connection with it ; although 

 we are under the impression that it was first given by him 

 in the American Journal of Mathematics. 



In a supplementary chapter some examples are given 

 of the application to electrical phenomena of the prin- 

 ciples of Carnot. Certain of these, due to M. Lippmann, 

 are ranged under the somewhat high-sounding title of the 

 Conservation of Electricity. We are a little inclined to 

 question the propriety of this phrase; but we are certainly 

 obliged to MM, Mascart and Joubert for a succinct 

 account of what we are to understand by it. 



We shall look with much interest for the second volume 

 of this work, in which, among other things of interest to 

 practical electricians, we are promised a discussion of the 

 efficiency of electric generators and electromotors, a sub- 

 ject on which the recent experience of the authors at the 

 Paris Exhibition must have well qualified them to give an 

 opinion. G. C. 



OUR BOOK SHELF 



Die Gasteropoden der Meeres-ablagerungen der ersten und 

 sweiten miocdnen mediterran-stufe in der Oesterreichisch 

 — Ungarischen Monarchic. Von R. Homes und M. 

 Auinger. Lieferung 1, 2, 3. (Vienna : Holder, 1879- 

 1SS2.) 

 A meritorious and useful contribution to our knowledge 

 of the tertiaries of middle Europe. The first-named 

 author is the worthy son of a worthy sire, the late Prof. 

 Homes, whose work on the fossil shells of the Vienna 

 Basin is so familiar to palaeontologists. The total number 

 of species hitherto described or noticed in the present 

 publication is 220, including 94 new species or forms. 

 Out of all this number 11 only are given as recent or 

 living ; and two more may be added (viz. Nassa semistriata 

 and Columbella cormgata of Brocchi), which inhabit the 

 Mediterranean as well as the North Atlantic. These recent 

 species have survived from the Miocene epoch — a period 

 of incalculably remote antiquity — without the slightest 

 change. The rest may be regarded as the ol irXeova in 

 the same sense as we use euphemistically for our dead. 

 Perhaps some more fossil species may be hereafter iden- 



