NATURE 



[June 25, 1908 



only the merely diagnostic literature, but all that 

 bears upon the subject, has been exhaustively studied. 



Among the most interesting sections is the one 

 bearing on the Syllids. It has long been known that 

 these Annelids are capable of asexual reproduction, and 

 that the buds so formed, on assuming maturity, carry 

 their eggs attached to their feet. Prof. Mcintosh 

 refers to several interesting cases of bud-formation. 

 Certain American species of Trypanosyllids, for 

 example, give rise to lateral buds, the stock assuming 

 a frond-like appearance. Mr. Crossland has found an 

 East African Syllid which has a crown of buds at its 

 hinder end, and other species which are parasitic on 

 Nemertines, Polychaets, and other hosts. There are 

 some thirty representatives of this family already 

 known from British waters, and their description and 

 changes of form on assuming maturity are full}' 

 dealt with. 



The distribution of these Polych^et Annelids will 

 undoubtedly form a most interesting mass of evidence 

 when it is collated. In its present form no conclusions 

 can be safely drawn. We can only say that manv 

 species have a very wide range, extending to both 

 sides of the Atlantic, and occurring as far north as 

 Greenland and as far south as the Falkland Islands, 

 whilst in some cases the same species is found both in 

 the Atlantic and in the Indian Oceans. It is also clear 

 that the British Polychaet fauna is probably as rich in 

 specific variety as that of any other coasts so far ex- 

 plored. The coasts of Ireland, though not so 

 thoroughly worked as those of the Channel or of the 

 east of Scotland, have yielded manv interesting forms, 

 and the careful comparison which the author has 

 instituted between specimens from different localities 

 and between those of our own and of other coasts is 

 but one instance of the careful discrimination and 

 comparison which distinguish the work. We are glad 

 to see that another part is ready for press, and we 

 hope that finrmcial aid will be forthcoming to com- 

 plete this monograph. 



DIRECT-CURRENT ELECTRICAL 

 ENGINEERING. 



Principles of Direct-current Electrical Engineering. 

 By J. R. Barr. Pp. viii-l-454. (London : Whittaker 

 and Co., igo8.) Price loi. net. 



A S the author states in the preface, this 

 ■^»- treatise was primarily written for the use 

 of intermediate classes in universities and technical 

 colleges, and is based on his lectures to second-year 

 students. It is intended to bridge the gap between 

 the several elementary manuals and the many works 

 on special branches, and in this object the author has 

 succeeded admirably. During the last few years in- 

 numerable books dealing with direct-current electrical 

 engineering have appeared, but they are either too 

 elementary or else too highly specialised. This book 

 deals chiefly with principles, but the author has kept 

 not only the theoretical, but also the practical 

 side of the question well in view. 



The first two chapters are devoted to the units em- 

 ployed in electrical engineering and the fundamental 

 NO. 2017, VOL. 78I 



principles, such as Ohm's law, the heating effect of 

 currents, &c., while the third chapter deals with 

 electromagnetism and the magnetisation of iron. 

 The latter chapter gives the student a clear insight 

 into the magnetic quantities underlying the design 

 of dynamos and motors. A short description is given 

 of Ewing's hysteresis tester and permeability bridge, 

 and the method of using it. 



About sixty pages are occupied with a discussion of 

 electrical measuring instruments. The principles 

 governing the construction of ammeters, voltmeters, 

 wattmeters, and electric-supply meters are set out in a 

 clear and practical manner, and even maximum- 

 demand indicators are briefly touched upon. 



Two chapters treat of storage batteries and electric 

 lighting, but these are rather disappointing. .Surely , 

 the short section dealing with metallic filament lamps 

 might have been amplified with some advantage, 

 especially considering the enormous progress made in 

 illuminating engineering. It is, further, somewhat 

 out of date to take up a section with a discussion of 

 37-volt osmium lamps. Practically speaking, these 

 lamps are not used at all, and in ail probability their 

 manufacture has been abandoned for some time. It 

 would have been better to have given us particulars 

 about the osram, wolfram, tungsten, and zircon-wol- 

 fram lamps, which are now made for 250-volt circuits, 

 and are of great practical importance. Open, enclosed, 

 and flame-arc lamps are briefly touched upon, as well 

 as illumination and photometry, but on the whole this 

 chapter is, as already said, rather unsatisfactory. 



Overhead and underground conductors, and the 

 principal methods of laying cables, as well as the cal- 

 culation of voltage drop in conductors, are next 

 described in about forty pages. 



The last six chapters of the book are devoted to 

 dynamo-electric machinery, its construction, design, 

 and operation, and these chapters are undoubtedly the 

 best in the book. The construction of armatures, 

 commutators, and brushes is very fully dealt with. 

 and the use of coloured diagrams used for illustrating 

 the various methods of armature windings should be 

 extremely useful to students. The theory of the mag- 

 netic circuit is gone into very carefully, and it will 

 give the student a clear insight into the calculations 

 required for tlie design of dynamo-electric machinery. 



The methods of determining characteristic curves, 

 parallel operation, and methods of voltage control are 

 also considered, while one chapter deals with motors 

 and controllers. The section on testing is very brief, 

 and it is hoped that in a next edition this may be 

 somewhat enlarged. 



In the last chapter we come to the subject of elec- 

 tricity control, and the author enters fully into the 

 points connected with switchboards. The section deal, 

 ing with fuses, circuit-breakers, lightning arresters, 

 and switches is excellent, and contains a large amount 

 of practical information. Various examples of switch- 

 board designs, illustrated by working drawings, com- 

 plete a very interesting chapter. At the end of the 

 book there is an appendix containing practical pro- 

 blems to be worked by the students. 



The author is to be congratulated upon the work 

 which he has produced. It is not too practical or tot) 



