NATURE 



341 



THURSDAY, JANUARY 3, 1918. 



ELECTRICAL ENGINEERING. 



(i) A Treatise on the Elements of Electrical 

 Engineering. A Text-book for Colleges and 

 Technical Schools. By William S. Franklin. 

 Vol. i., Direct- and Alternating-current Machines 

 and Systems. Pp. x + 465. (New York: The 

 Macmillan Co. ; London : Macmillan and Co. , 

 Ltd., 1917.) Price 245. net. 



(2) Continuous-current Motors and Control Appa- 

 ratus. A Practical Book for all Classes of 

 Technical Reader. By W. Perren Maycock. 

 Pp. xvi + 331. (London: Whittaker and Co., 

 1917.) Price 65. net. 



(3) Power Wiring Diagrams. A Handbook of 

 Connection Diagrams of Control and Protective 

 Systems for Industrial Plants. By A. T. Dover. 

 Pp. XV + 208. (London: Whittaker and Co., 

 191 7.) Price 6s. net. 



(i) TT is usual for writers of books on electrical 

 ■'- engineering to confine themselves to the 

 theory either of direct-current or of alternating- 

 current practice. In an elementary treatise, how- 

 ever, it is best to include both, and this the author 

 has done. A most satisfactory feature is the intro- 

 duction of the concepts of the modern theory of 

 electrons, and this greatly stimulates the interest 

 of the reader in many of the phenomena and appa- 

 ratus described. Other excellent features are a 

 free use of the calculus — we were impressed by the 

 pain§ taken to make the mathematics simple — and 

 the introduction of many easy problems. 



After the table of contents. Prof. Franklin gives 

 a list of the national organisations and societies in 

 America relating to engineering, and describes the 

 field in which each society /is specially interested. 

 The student is encouraged to obtain further infor- 

 mation .directly from the secretaries of these 

 societies. In particular, he is advised to write to 

 the Bureau of Standards at Washington to obtain 

 a list of its publications and full information about 

 its activities. This is very properlv regarded as 

 an essential part of the education of an American 

 engineer. 



In the first few chapters a resume is given 

 of magnetism and electrodynamics. In several 

 places the author has abbreviated his explanations 

 until they are obscure. We read, for example, 

 on p. 73 that when a circuit has a certain induct- 

 ance " one volt will cause the current in the cir- 

 cuit to increase at the rate of one ampere per 

 second." The uninitiated reader would naturally 

 think that the current goes on continually increas- 

 ing so long as the volt is applied in the same way 

 as the velocity of a mass of one gram goes on con- 

 tinually increasing when a dyne is applied to it. 



The author is hamoered bv his loyal adherence 

 to the nomenclature list published by the American 

 Institute of Electrical Engineers. For instance, 

 he calls the unit of the flux of magnetic induction 

 the maxwell, and the unit of magnetic induction 

 density the gauss. We deduce also that a gauss 

 NO. 2514, VOL. 100] 



is both a gilbert per centimetre and a maxwell per 

 square centimetre. It seems to us that there is a 

 quite unnecessary dragging in of the names of 

 great men of science, especially as the definitions 

 are framed on the assumption that permeability is 

 a simple numeric. Clerk Maxwell would not have 

 admitted this assumption. The American gauss 

 is the unit both of magnetic induction and of 

 magnetic force. Many physicists consider that 

 magnetic induction is caused by magnetic force 

 just as strain is caused by stress. The assumption 

 that cause and effect are measured in the same unit 

 ,is unjustifiable. 



In our opinion the practice of christening units 

 after the names of men of science should be adopted 

 only very sparingly. The watt and the joule are 

 well named, but we deprecate the growing use of 

 the kelvin for the unit in which electrical energy 

 is bought and sold. Those evil-sounding words, 

 also, the abohm, the abampere, and the abfarad, 

 used by Americans are almost libellous to the great 

 men whose memory th^y are supposed to keep 

 green. 



On p. 96 a table of sparking distances is given 

 between spherical electrodes the diameters of which 

 are 0*5, i, 2, and 5 cm. respectively. The room 

 temperature at which the experiments were made 

 was 18° C, and the reading of the barometer 

 745 mm. Analysing the figures given, we find 

 that for a given pair of electrodes the spark occurs 

 very approximately when the maximum potential 

 gradient between them attains a certain definite 

 value. Surely the author should have pointed this 

 out. It is a physical fact of great interest and 

 may well prove to be the starting point of new 

 advances in our knowledge. It is at least of 

 practical value to be able to calculate the sparking 

 distances between spheres and the voltages at 

 which the brush discharges begin to appear on 

 them. 



The chapter on the electron theory is clearly 

 written, and much knowledge is given in little 

 compass. We are sorry that Peek's formula for 

 the voltage at which the corona appears on 

 cylindricar wires is not given, as it is wonderfully 

 accurate and most useful to power engineers. 

 Descriptions are given of Cottrell's apparatus for 

 precipitating dust and smoke particles from the 

 atmosphere, and of ozonisers for converting 

 oxygen into ozone. But the most interesting 

 devices described are the vacuum-tube current 

 valves the action of which depends on the emis- 

 sion of electrons by hot bodies. These current 

 valves are now much used as receivers and 

 detectors in radlotelegraphy, and also as " ampli- 

 fiers " either for exciting or for maintaining 

 electric oscillations. 



In those parts of the book devoted more parti- 

 cularly to engineering the author describes the 

 latest types of electrical machines, and it'is satis- 

 factory to notice how well they illustrate funda- 

 mental principles, and how amenable their theory 

 is to elementary mathematical treatment. The 

 series parallel controller, the rotary converter, the 

 frequency transformer, and all the various types 



T 



