January 19, 1893] 



NATURE 



269 



its details are already familiar, the picturesque clearness 

 with which they are presented will make their knowledge 

 more real and more complete. The standard of excel- 

 lence maintained in the lectures makes distinction diffi- 

 cult and invidious, or we would distinguish the lectures 

 on Xewton and those on tides as models of what such 

 popular scientific expositions should be. The book is 

 copiously, and, on the whole, well illustrated, but some of 

 the illustrations — notably those of clusters and nebulas — 

 are very familiar and somewhat out of date. A curious 

 mistake occurs on page 291, where a well-known draw- 

 ing of a comet appears as an " old drawing of the Andro- 

 meda nebula." The illustration on page 326, showing 

 the patns of Uranus and Neptune and their relative 

 positions from 1781 to 1840, and professing " to illustrate 

 the direction of their mutual perturbing forces," is partly 

 misleadmg ; but in introducing this Dr. Lodge has 

 erred in good company, for the diagram, originally due to 

 Dr. Houghton, appears in many of our recent astronomical 

 text-books. A. T. 



Electric Lighting and Power Distribution. Part I. By 

 W. Perren Maycock, M.I.E.E. (London: Whittaker 

 and Co., 1892.) 

 This cheap and useful little text-book has been written 

 for the author's junior students, as he is of opinion that 

 no trustworthy elementary work on the subject is to be 

 obtained. The scope of the work has been limited to 

 the syllabus of the ordinary grade examination of the 

 City and Guilds of London Institute. We find, however, 

 much information on subjects not usually found in other 

 manuals. The book is freely illustrated, and the de- 

 scriptions are clear. 



It is very important for the junior student to under- 

 stand clearly what is meant by a line of force, and to 

 grasp the fact that lines of force are only assumed to 

 exist, because, by such an assumption it is possible to 

 explain many, otherwise inexplicable, phenomena. On 

 page 47 we find the following statement : — " The power 

 which any magnet possesses, of picking up pieces of 

 iron, and of acting upon another magnet, depends 

 upon the existence of lines of magnetic force." This 

 quotation is vague ; a junior student might easily 

 imagine that the lines of force really existed, whereas 

 they are purely assumptions, to elucidate the pheno- 

 mena of magnetic attraction. The illustrations of 

 simple bar magnets, solenoids, and electro-magnets, in 

 which the lines of force are delineated, should have the 

 assumed directions of the lines of force clearly shown by 

 arrow-heads. This might be done with advantage in 

 Figs. 17 to 20. 



Chapter IV. deals with induction of currents, electro- 

 magnetic induction, Faraday's Law, and concludes with 

 a clear description of magneto-motive force, magnetic 

 resistance, magnetizing force, induction and permeability. 

 These latter are very difficult for a junior student to 

 understand thoroughly, and the author should have 

 devoted more space to the discussion of these important 

 points in dynamo construction. One particularly good 

 feature in this text-book is the large number of questions 

 arranged at the end of each chapter. These are well 

 suited to test the knowledge of a student. Chapter V. 

 deals generally with electrical testing, measuring instru- 

 ments used in installations, and meters for measuring 

 the current, such as Teague's, Elihu Thomson's, and the 

 Wright- Ferrauti. Chapter VI. concludes the book, de- 

 scribing the principle of the dynamo, different types of 

 machines, and the construction of the various parts. 



Taken as a whole tiiis book attempts too much. The 

 matter described has suffered considerably by condensa- 

 tion, a serious thing where junior students are concerned. 

 Most of the illustrations are good ; some are indis- 

 tinct, and Fig. 98 is decidedly wrong, showing the brushes 

 set tor one direction of rotation, and the arrow indicating 

 the reverse. 



NO. I 2 r 2, VOL. 47] 



On the other hand the sequence of matter is good, 

 and a student should learn much from the work. The 

 author takes great pains to describe clearly the many 

 units involved, particularly the applications of Ohm's 

 law. The book would last much longer in the hands of 

 the average student if the present paper binding were 

 replaced by something stronger. 



The Naturalist on the River Amazons. By Henry 

 Walter Bates, F.R.S. With a memoir of the author 

 by Edward Clodd. Reprint of the Unabridged 

 Edition. With Map and Numerous Illustrations. 

 (London : John Murray, 1892.) 

 Thls work is so well known, and has long held so high a 

 place among scientific books of travel, that it is unneces- 

 sary to do more than note the appearance of a new 

 edition. It is clearly printed on good paper, and the 

 illustrations are well reproduced. The introductory 

 memoir by Mr. Clodd is a most welcome record of the 

 main facts of Mr, Bates's career. The materials for this 

 interesting sketch were enriched by letters placed at the 

 author's disposal by Sir Joseph Hooker and Mr. Francis 

 Darwin. An excellent portrait of Mr. Bates is included 

 in the volume. 



LETTERS TO THE EDITOR. 



L The Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of Nature. 

 No notice is taken of anonymous communications. '\ 



A Proposed Handbook of the British Marine Fauna. 



Such a handbook as Prof. Herdman suggests is so much 

 wanted that many naturalists must from time to time have felt 

 tempted to essay it. But the difficulties are very formidable. 

 Prof. Herdman seems to contemplate the preparation of such a 

 work mainly as a labour of compilation. But the groups where 

 compilation would nearly suffice are just those where the hand- 

 book is least required. On the other hand, such a group as the 

 Amphipoda, in spite of Canon Norman and Mr. Stebbing's 

 many papers, is still in great need of revision ; it was only the 

 other day that Canon Norman opened our eyes to our rich fauna 

 of Mysidae, before which time no search among published records 

 would have told us anything worth the having ; we are in just 

 the same position as to our British Cumacea, until Canon Norman 

 again reveals the treasures of his cabinet ; our Pycnogrns are 

 almost as little known. In every one of these groups, and in 

 many others like them, the preparation of a hand-list would need 

 the experience of a specialist, just as much as the Tunicata would 

 require Prof. Herd man's own special knowledge. The area to 

 be embraced is another difficulty. Prof. Herdman proposes to 

 take the British area as defined by " Canon Norman's" B.A. 

 Committee in 1887, on which he himself served. But the com- 

 mittee's report was repudiated by Canon Norman himself, who 

 afterwards suggested a wider " British area," whose boundaries 

 I fancied had since been recognized as more suitable by every- 

 body. However the British area be defined, there will long 

 remain a difficulty in the numerous forms not yet recorded from 

 within it, but which are likely, or certain, to turn up when sought 

 for. Such things as the parasitic and other Crustacea described 

 of late years by Giard and his pupils from Wimereux form a 

 case in point. I am inclined to think that to make in the first 

 instance a hand-list of the whole fauna of the North Atlantic 

 basin would be not a bit more difficult, but in some respects 

 easier, than to restrict the list to the British area alone. That 

 it would be incomparably more useful is certain. It would make 

 a book not more than three times (perhaps little more than twice) 

 as big as Carus's "Fauna Mediterranea." And it would.be a 

 very important step towards that new systema naturcc of which 

 the Germans are already beginning to talk, and which it is high 

 time were begun. 



But Prof. Herdman both asks discussion of his plan, and also 

 invites criticism on his execution of it. Take his very first illus- 

 trative genus, which he tabulates as follows : — 



Antennularia. — Stems simple or branched ; pinnas verti- 

 cillate ; nematophores along the stems ; gonothecas axillary, uni- 

 lateral. 



