November 4, 1922] 



NA TURE 



595 



Applied Electricity. 



A Dictionary of Applied Physics. Edited by Sir 

 Richard Glazebrook. Vol. II. Electricity. Pp. 

 vii + 1104. (London: Macmillan and Co., Ltd., 

 1922.) 635. net. 



IT is interesting to compare the second volume of 

 Sir Richard Glazebrook's " Dictionary of Applied 

 Physics " with the electrical portions of older diction- 

 aries. For example, in Barlow's " Dictionary of Pure 

 and Applied Mathematics " (1814) it is said that " the 

 science of electricity became a general subject of con- 

 versation " after the discovery of the " Leyden Vial." 

 In Nichol's " Cyclopaedia of the Physical Sciences " 

 (i860) we learn that electrical science " has spoken for 

 itself to the world as no other has." " Witness the 

 simultaneous discovery of the Leyden Phial and the 

 Electric shock." Three practical applications of 

 electricity are given, namely, the lightning-conductor, 

 the electric telegraph, and electroplating. The last 

 is specially commended as being " so conducive to 

 the comforts and elegancies of life." An examination 

 of the volume under review will show how greatly 

 our knowledge has been widened during the last sixty 

 years. We were sorry, however, not to have seen 

 the " Leyden Jar " mentioned. 



The plan of the dictionary follows to a certain extent 

 that adopted by Nichol, but the important sections 

 are much larger. In fact, quite substantial books 

 could be made of the sections written by some of the 

 contributors. Besides the important contributions 

 there are a few short articles and many definitions 

 of electrical quantities, machines, instruments, and 

 methods. The absence of an index makes it difficult 

 to find out whether any subjects have been omitted 

 or not. There is a very elaborate name-index, but 

 this will be little help even to the older physicist or 

 electrician, as many of the names will be unknown 

 to him. We think that the younger physicist will 

 have considerable difficulty in finding out what he 

 wants. Doubtless, this will be remedied when the final 

 volume is published. We have not noticed anything 

 about electric traction, electric ship-propulsion, electric 

 vehicles, lightning-conductors, rotary and frequency 

 converters, electrostatic machines, the attraction 

 between electrified spheres, or the fixation of nitrogen. 

 We take it that atmospheric electricity will come under 

 meteorology in the next volume. 



We were glad to notice that the contributors had 

 not been handicapped by being compelled to adopt 

 a rigid nomenclature and an invariable set of symbols. 

 As a rule, those agreed on internationally have been 

 adopted. Although considerable use has been made 

 throughout of elementary vector analysis, there is 

 NO. 2766, VOL. I 10] 



little demand made on the reader's knowledge of 

 mathematics. Academical subjects, like spherical 

 harmonics and the perennial " electrified ellipsoid," 

 have been omitted. 



Dr. Rayner has written a useful section on alternat- 

 ing-current instruments and measurements. He has 

 made a happy selection of the best modern measur- 

 ing instruments. His description of the electrostatic 

 watt-meter is specially good. Occasionally his strain- 

 ing after conciseness leads him into inaccuracy ; as 

 when he says (p. n) that the torque is equal to the 

 square of the volts instead of being merely proportional 

 to that quantity. There is a misprint also in the 

 equation on this page. The articles on primary 

 batteries, accumulators, and cables are good, but the 

 last could have been expanded with advantage. The 

 assumption on p. 94 that the thermal emissivity is 

 independent of the radius of the wire is certainly not 

 true, and we doubt whether the formulas given on 

 p. 95 are of general application. 



Mr. Albert Campbell contributes a valuable article 

 on electrical capacity and its measurement. He 

 generally refers to capacity as " capacitance," which 

 is the name the Americans now use, and he calls the 

 capacity between two conductors the " working 

 capacity." He clearly recognises the difference be- 

 tween two of the various kinds of capacity and calls 

 them by different names. In other parts of the volume, 

 however, which capacity is meant is not so clear. For 

 example, under units (p. 948), we read that a con- 

 ductor which had a capacity of 1 farad " even though 

 composed of plates very close together, would be very 

 large." It looks as if conductor were a^ misprint for 

 condenser. The various kinds of capacities have been 

 clearly defined by nomenclature committees of the 

 Physical Society and of the Institution of Electrical 

 Engineers. On p. 107 formula; for the capacity 

 between two circular plates and the capacity to earth 

 of one of them are given; the formula? are only 

 approximations and no limitations to their accuracy 

 are given. Their value is therefore doubtful. We 

 note misprints in formulas (27), (50), (54), and (55). 



T. Gray's results for the dielectric strengths (now 

 usually called the electric, strengths) of air at different 

 thicknesses are given. We think that this is a mis- 

 leading way of interpreting the experimental results. 

 If we consider spherical electrodes in air, the disruptive 

 voltages are computed in everyday work from their 

 distance apart and their radii, with a maximum in- 

 accuracy of about 1 per cent. From these experiments 

 we would conclude that the assumption that the 

 electric strength of air was 27-4 kilo volts per cm. at 

 25° C. and 76 cm. pressure, whatever the thickness 

 of the layer might be, would lead to very approxi- 



