October 8, 19 14] 



NATURE 



143 



an armature core; from p. 81 that the correct 

 position for the brushes never depends on the load ; 

 and from p. 85 that the heating of a continuous- 

 current armature is the only thing which limits 

 its output. 



The book is well illustrated, both by diagrams 

 and half-tone blocks. The latter have mostly 

 been derived from the literature of the large 

 American manufacturing companies, but they have 

 been well chosen; in a few cases only, mostly of 

 instruments, do they show too little detail for the 

 purpose in view. The British reader must, of 

 course, remember that the book is American, and 

 that the statements as to standards and regula- 

 tions do not necessarily apply to this country. 



(3) This book appears to be specially written 

 for use in the author's own laboratory, and we 

 scarcely think it will be of much service elsewhere. 

 It deals with twenty experiments on continuous- 

 current machines and apparatus, and ten on alter- 

 nating-current ones. It can scarcely be said to 

 describe them, and it certainly does not give those 

 useful practical hints which every laboratory in- 

 structor knows to be necessary to enable even the 

 best students to carry out their work successfully. 

 The student is referred to another book for prac- 

 tically everything in the way of information ; as 



|we have not seen that book, perhaps it would not 

 quite fair to criticise this one in detail. But 

 ^e must confess that except in special circum- 

 stances we should never think of using iio-volt 



imains for measuring the resistance of a yard or 

 ^o of wire or of the armature of a dynamo, nor 



[pf complicating matters by the addition of a short- 

 fircuiting switch for every ammeter. On the other 

 land, we should certainly specify the use of fuses 

 \o guard against accident, although the author 

 )mits them from his diagrams and instructions. 



(4) This excellent little book is a collection of 

 Formulas for calculating the voltages and currents 

 It any point in a power transmission line the loads 



id constants of which are known. It is more a 

 preference book for engineers who have to make 

 ^uch calculations than a text-book for students, 

 ^ut to those of the latter who wish to get up this 

 irticular work we can highly commend it. Fol- 

 )wing an ingenious chart from which the desired 

 isults can be read off with sufficient accuracy in 

 le case of short lines, we are given, in tabular 

 )rm, sets of formulas of increasing degree of 

 xuracy to suit the chief cases which arise. The 

 lits of application are carefully indicated in 

 ich case. 



Part ii. gives an account of the theory on which 

 lese formulas are based ; this portion is a model 

 \i conciseness combined with lucidity. Part iii. 

 NO. 2345, VOL. 94] 



is a repetition of the tables of formulas, with the 

 addition of tables of constants of copper and 

 aluminium cables for the American standard fre- 

 quencies of 25 and 60 cycles per sec. 



(5) This book is non-mathematical and can be 

 thoroughly recommended to those for whom it 

 was written. It gives a very good account of the 



I Marconi system, and also of the various other 

 I ones about which the public have lately heard so 

 ! much. With few exceptions, the descriptions are 

 good and the illustrations are excellent. We 

 should have liked a rather better elementary 

 account of the production of oscillations and of 

 the emission of waves from the oscillator, and 

 also a more convincing explanation of the action 

 of the Marconi magnetic detector. Nor can we 

 imagine any reason for the peculiar connections 

 given on p. 50 for a shunt-wound motor starter. 



(6) We wish we could compel all architects, 

 wiring contractors, shopkeepers, and users of 

 electric light generally to read this little book. 

 We might then have fewer glaring (in more ways 

 than one) examples of how not to arrange artificial 

 illumination. The book contains little about the 

 construction of the lamps, but gives an excellent 

 account of their characteristics and of the prin- 

 ciples which must be followed if a pleasing result 

 is to be obtained from their use. 



David Robertson. 



CELESTIAL MECHANICS. 

 An Introduction to Celestial Mechanics. Second 

 revised edition. By Prof. F. R. Moulton. 

 Pp. xvi + 437. (New York : The Macmillan 

 Co.; London: Macmillan and Co., Ltd., 1914.) 

 Price 155. net. 



THE appearance of Prof. Moulton *s intro- 

 ductory treatise on dynamical astronomy 

 in a second edition is a sufficient proof that the 

 work, which was first published twelve years ago, 

 has satisfied a certain demand. This is very 

 natural, for there is no similar book which covers 

 the same ground. After the revision which it 

 has now undergone it should prove even more 

 useful than in its original form. The author's 

 aim has been to give the student that general 

 view of the whole subject, so far as it can be 

 treated by fairly elementary methods, from which 

 Tie may pass on, if he pleases to go further, to 

 the technical details which are to be found in 

 treatises on " Bahnbestimmung," or to the refined 

 mathematical processes which are developed in 

 theoretical works on celestial mechanics, or in the 

 original memoirs of the great masters. 



The early chapters develop the problem of two 

 bodies in undisturbed motion. They lead up 



