September 2, 1915] 



NATURE 



knowledg^e or ability of the student. We have 

 tested the numerical accuracy of the answers given 

 to several of the problems with satisfactory results. 



(2) Mr. H. B. Dwight is the electrical engineer 

 to the Canadian Westinghouse Company, and is 

 one of the greatest authorities on long-distance 

 power transmission. To the reader conversant with 

 the technicalities of electrical engineering this book 

 can be warmly recommended. The author points 

 out the advantages of using special synchronous 

 motors to keep the voltages at the distributing 

 stations constant under all conditions of load. 

 By this means the radius of action of electric 

 " power transmission can be very considerably in- 

 creased. The main advantage gained by this in- 

 crease of distance is that it renders possible the 

 linking together of large networks either directly 

 or by suitable "frequency transformers." The 

 economies rendered possible by this procedure are 

 well known and much thought about by electrical 

 engineers. Unfortunately the main difficulties in 

 linking up all the supply companies in London 

 have to do with the vested interests concerned and 

 the inherent conservatism of station engineers. 



In America there are several large networks 

 already in existence. In North and South Caro- 

 lina, for instance, over a thousand miles of 100,000- 

 volt transmission lines are now linked together, the 

 lines stretching across 800 miles of country. The 

 Pacific Gas and Electric Company of California 

 has a network of 1500 miles, part of it being at 

 60,000 and part at 100,000 volts. It is highly 

 probable that even this extended supply of "elec- 

 tricity in bulk " will seem quite small in a few 

 years' time, as some of the many schemes pro- 

 jected for linking up systems of electric railways 

 are sure to be carried out. Mr. Dwight's book, 

 therefore, discusses a problem of great com- 

 mercial and economic value. In discussing the 

 more technical side of the problem Mr. Dwight 

 uses complex hyperbolic operators, and has been 



Ircessful in considerably simplifying the usual 

 Btment. 

 ij) Mr. W. Perren Maycock's book is intended 

 [an introduction to alternating-current work, 

 e diagrams are beautifully clear, the apparatus 

 described is all useful and fundamental, and the 

 descriptions are good. Simplified vector diagrams 

 are given. Many will find this work useful as an 

 introduction to more advanced treatises. 



The defects of the book are due mainly to an 

 attempt to explain to the non-mathematical reader 

 certain steps in the proofs of physical theorems 

 which demand mathematical knowledge. Unless 

 these steps are proved rigorously it does not seem 

 ■worth while to give them. No proof, for instance, 

 i-^ given that when the voltage follows the har- 

 NO. 2392, VOL. 96] 



monid law its effective value equals I'li times 

 its average value. To assume this, and to point 

 out in reasoning backwards that 



I'll =o"707/o'636 = 7r/(2v/2), 

 is rather a futile proceeding. It would be better 

 to state definitely that the value I'li used by the 

 designer of alternating-current apparatus is ap- 

 proximately equal to 7r/(2\/2), which is the value 

 deduced theoretically from the properties of the 

 sine curve. 



(4) From the point of view of the teacher, the 

 chief merit of Mr. Finn's book is its thoroughly 

 practical nature. Assuming that the physical 

 laboratory is fitted with the electric light, he shows 

 that many excellent and instructive experiments 

 can easily be arranged for junior students. The 

 student will appreciate the notes on . heat and 

 dynamics which are freely interpolated throughout 

 the text. The introduction and explanation of 

 technical terms in common use are innovations 

 which are to be commended. Everyone should 

 know what is meant by an adapter, a wall-plug, 

 a kilowatt-hour, bayonet and screw cap lamp- 

 holders, etc. We think also that all teachers 

 should know what is meant by "earthing," and 

 that one of the mains of the supply company is 

 usually earthed. Electrical students have generally 

 very hazy notions about what is meant by the 

 potentials of the supply mains. They seem to have 

 acquired at school the notion that difference of 

 potential is the only thing that need be considered, 

 and that the absolute value of the potential is of 

 no consequence. A good teacher could easily 

 explain the fallacy of this by pointing out how 

 workmen sometimes get dangerous shocks owing 

 to neglect of certain very elementary precautions. 



In one or two places the author's experiments 

 are perhaps too elementary. For example, it 

 seems unnecessary to prove that the currents in 

 conductors in parallel are not always equal to one 

 another. In some places the wording is clumsy. 

 On p. 374, for instance, instead of saying "the 

 bigger is the dielectric strength said to be," it 

 would be better to say "the greater the electric 

 strength." We are told that the "dielectric con- 

 stant" of a medium "varies somewhat with the 

 length of time for which the E.M.F. is applied." 

 Whether this is true or not depends on how we 

 define the dielectric constant. It certainly varies 

 with temperature. Everyone must perforce admit 

 that it is not a constant. It seems foolish, there- 

 fore, for physicists to go on calling it a constant. 

 The terms inductivity, dielectric coefficient, and 

 S.I.C. are in use. There is no excuse therefore, 

 for using the word " constant " for a variable 

 quantity. 



After defining the electrostatic unit of potential, 



