148 



NA TURE 



[June 15, i$82 



descent with the Germans, and all our well-founded 

 appreciation of their excellence, we weary of their very 

 virtues. One turns from their copious Griindlichkeit, as 

 from the indispensable labour of life, and one finds in the 

 reading of a goodFrench text-book a never-failing 

 pleasure. 



Only the first volume of the Lecons is as yet before us, 

 and some of our criticisms may have, on that account, 

 to be taken with allowance ; for the head, however im- 

 portant, is not the whole body. We see at once that 

 there is little in common between them and the " Electri- 

 city Statique ; " the plan of the work, so far as it has gone, 

 is quite different. It originated, so the preface tells us, in 

 the lectures of one of the authors at the College de 

 France. The first volume is general and theoretical ; the 

 second is to be special and practical. As to the propriety 

 of such an arrangement, much depends on the class of 

 students to which it is addressed. If it is meant for such 

 as have already a considerable knowledge of electrical 

 phenomena, and some practice in accurately conceiving 

 and describing them, then the plan is good. If, on the 

 other hand, the reader is supposed to be a beginner in 

 electrical science, knowing nothing of the phenomena, 

 but furnished merely with the requisite mathematical 

 knowledge, then we do not think well of it. We prefer in 

 that case, the arrangement of the " Electricite" Statique," 

 that is, a fuller account of the phenomena upon which 

 the fundamental principles rest, with a mathematical 

 treatment sufficient to prevent vagueness of impression, 

 and thereafter a detailed deductive account of the con- 

 sequences of the fundamental principles, and a full de- 

 scription of the phenomena irrespective of their agreement 

 or disagreement with theory. Assuming that we have to 

 deal with a student, who has the first element of a physi- 

 cist, viz. a tolerable mathematical education, perhaps the 

 greatest danger to be avoided is formalism, or blind 

 swearing, in verba magistri. Nothing is more likely to 

 encourage this, than hurried and hasty discussion of 

 fundamental facts. Nothing in reality is gained by 

 driving the learner express to the law of the inverse 

 square, and then leisurely expounding its consequences. 

 Far better, that we should first secure for him a thorough 

 qualitative understanding of the natural phenomena ; and 

 then teach him how they can be built together upon an 

 abstract frame-work, whose lines they will follow, not 

 necessarily with absolute coincidence. The learner must 

 be taught at the very outset that analysis is the servant and 

 not the master of the physicist ; and that a physical idea 

 is not always simplified by clothing it in an analytical 

 suit of buckram. This much as a warning to possible 

 students of this volume. 



With one feature of the plan of these Lecons we must 

 express unqualified satisfaction ; that is the adoption of 

 the methods of Thomson and Maxwell. At times these 

 are so closely followed that the paragraphs are little more 

 than translation ; at other times considerable changes, 

 chiefly in the way of simplification, are introduced. 

 At the same time, the authors have not scrupled to borrow 

 from other sources, where good material was to be had. 

 They have gone on the principle of Moliere, "je prends 

 mon bien oil jc le trouve " ; and rightly, for scientific light 

 (unlike political or theological), is not supposed to be the 

 property of one sect or one country. The English reader 



will not find much that is new, or perhaps we should say 

 not accessible to him in his own language, however much 

 he may learn as to arrangement and demonstration. 

 Originality apparently is not aimed at ; the authors 

 put before their readers such of the modern develop- 

 ment of electrical theory as they deem most impor- 

 tant in themselves, or most likely to be useful to the 

 physicist. We are of opinion that their selection on the 

 whole has been judicious ; and therein lies the chief merit 

 of the book. It will, therefore, fill a great gap in French 

 scientific literature. Possibly the second volume may 

 help to fill the corresponding gap in the experimental 

 part of the subject, which exists, unfortunately, in English 

 as much as in French literature. 1 How urgently such 

 treatises are wanted, and how ignorant one nation may be 

 of what is common-place to another, is well exemplified 

 by the fact that a distinguished savant like Prof. Clausius 

 lately published, both in Wiedemann's Annalen and in 

 the Philosophical Magazine, as something new and note- 

 worthy, the theorem of mutual potential energy and cer- 

 tain consequences therefrom, that have been familiar to 

 us ever since we knew anything of electrical theory, i.e. 

 some ten years or more. 2 



We are thus led to notice the one serious defect of this 

 treatise — the entire want of all references to original 

 sources of information. These Lecons can have been 

 meant only for those that contemplate a special study of 

 electricity or original work of some kind bearing upon it ; 

 for such learners knowledge at first hand in some degree is 

 essential ; and who is to lead the scientific sheep to the 

 water-springs if their responsible shepherds do not ? We 

 are well aware, from bitter experience, of the drudgery in- 

 volved in this part of book-making, and of the difficulty, 

 with all care, of being absolutely accurate and just ; but 

 utter neglect of the duty is inexcusable. Here is a pro- 

 voking instance. The reader is aware that there are two 

 different ways of representing the action of a mass of 

 polarised molecules : — First, by a volume and a surface- 

 distribution of attracting centres ; second, by a surface 

 distribution alone. The first of these is undoubtedly due 

 to Poisson. The second is continually used in German 

 books, and attributed to Gauss (the first method, and 

 Poisson with it, they mostly ignore). Now MM. Mascart 

 and Joubert add to the diversity by quoting the second 

 method as Poisson's. It is certainly news to be told that 

 Poisson knew of any such general theorem, and a cursory 

 re-examination of his memoirs failed to find it. Until the 

 exact reference is given, we must hold our previous con- 

 viction that the theorem in question was virtually first 

 given by Green in his essay on " Electricity and Mag- 

 netism" (Nottingham, 1828). It was discovered inde- 

 pendently by Gauss, whose statement of it (the first 

 explicit one) is given in Art. 2, " Intensitas Vis Magnetics, 

 &c," read December, 1832, to the Royal Society of 

 Gottingen. His demonstration is given in Art. 36 of 

 the "Allgemeine Lehrsatze, &c." Again, the corollaries 

 from Gauss' Theorem of Mutual Potential Energy in Art. 



1 The Germans have the admirable treatise of Wiedemann, which, in its 

 forthcoming shape, with electrostatics added, will be the greatest experi- 

 mental treatise on elcctrici.y in existence. 



2 The theorem is simply a particular discrete form of Green's theorem ; 

 and in this shape was originally given by Gauss in his "Allgemeine Lehr- 

 satze, &c." In one point of view it is simply a property of homogeneous 

 functions of the second degree, and plays a part in many branches ol 

 mathematics, e.g. curves and surfaces of the second degree, theoreticaf 

 dynamics, strains and stresses, &c. 



