October i8, 1894] 



NATURE 



59' 



Then, again, the passage of aims between the author 

 and Dr. Neuhaus in this same chapter, and Herr Hruza 

 (chapter xxviii.) and, above all, Mr. Ives (pp. 239-240), 

 is conducted in a manner that in this country would be 

 regarded as very bad form. Perhaps German notions of 

 scientific literary taste differ from ours, but the writer of 

 this notice has never yet come across a German work 

 professing to be a scientific te.\t-book, in which such bad 

 taste is shown as in the introduction of the personalities 

 which are here indulged in.' Discounting these im- 

 perfections. Dr. Vogel is to be congratulated on this 

 second instalment of his book ; it will be found valuable as 

 a compilation, and still more valuable as embodying much 

 original work. No scientific student of the subject can 

 dispense with it, and beyond the domain of pure photo- 

 graphy the chemist and physicist will find much in its 

 pages worthy of consideration. R. Meldola. 



THE MEASUREMENT OF ELECTRICAL 

 RESISTANCE. 



A Treatise on the Measurement of Electrical Resistance. 

 By William Arthur Price, M.A., A..M.I.C.E. (Oxford : 

 Clarendon Press, 1894.) 



OF all electrical measurements probably that of 

 measuring a resistance is the most important, 

 since the resistance of many bodies is a permanent 

 quality, and resistances can be compared by means of 

 apparatus of comparatively simple construction, while the 

 results obtained are much more accurate than in the case 

 of any other electrical measurement. Most books on 

 practical electricity contain more or less complete de- 

 scriptions of the methods generally employed in the 

 measurement of resistance, and in some cases give what 

 may be called "diagrammatic" descriptions of the con- 

 struction of the different forms of apparatus employed. 

 The work under consideration, however, goes much 

 further, for in it the mechanical details of the construc- 

 tion of the apparatus are described in a manner which 

 shows that the author is practically acquainted with his 

 subject. 



The book may be roughly divided into two parts : in 

 the first of these the materials used in the construction 

 of resistances and the different methods of winding and 

 mounting resistance coils are fully dealt with ; while the 

 second part contains full descriptions of the methods 

 ordinarily employed in the measurement of resistances, 

 both high and low. 



The first chapter is introductory, and contains a de- 

 finition of the term resistance, while the conditions to be 

 fulfilled by a material suitable for the construction of 

 standard resistances are shortly discussed. The proper- 

 ties of the different alloys employed in the construction 

 of resistances are fully dealt with in the second chapter. 



After referring to the artificial " ageing " of manganine 

 wire, and to the extremely small value of the thermo- 



1 Out of con>Ukration for those concerned, I rcfi.lin from K'vipg speci- 

 nieos of the par;i-.;raphs complained of. Can it be that the style of discussion 

 is incidental to the subject? Similar lucubrations arc soaietimcs to be seen 

 embellishing (?; the pages of photogfaphic journals. In passing the .-ibove 

 strictures it is to be understood that the que-lion of the author or his an- 

 tagonists being right or wr..nE is not rai.^ed : it is the st\le which is objected 

 to- the transference of personal polcmici from journals in which they; mij^ht 

 possibly be tolerated, to the p.tgcs of a text-book in which they are intoler- 

 able. 



NO. I 303, VOL. 5 O] 



electric force between this alloy and copper, the author 

 says that the electrical properties of this material seem 

 to be quite permanent. This opinion, however, is at 

 variance with the experience of most people who havs 

 tested this alloy, and it would be of interest to know 

 whether any satisfactory experiments have been made to 

 settle this point. Although it may be important in many 

 commercial operations, where accuracy is not so much 

 aimed at as simplicity and freedom from troublesome 

 corrections, to make resistances of alloys having a low 

 temperature coefficient, yet in any experiment where 

 accuracy is necessary it is much more important to have 

 a constant and linear function for the temperature cor- 

 rection than to have an extremely small but variable and 

 uncertain one. A comparison of the curves for the 

 variation of the resistances of the different alloys, which 

 have been reproduced from Profs. Dewar and Fleming s 

 paper, shows at once the fatal objection to manganine. 

 Another objection to this alloy, as at present manu- 

 factured, is the extreme variation in physical properties 

 between the different samples supplied. 



Two very interesting chapters are devoted to the 

 construction of resistance coil bobbins, and the 

 methods employed for winding the wire. In con- 

 nection with the question as to the best form to give 

 standard resistance coils in order that the temperature 

 may be accurately known, the author recommends that 

 the coil be enclosed in a thick copper case, with a recess 

 filled with mercury for the insertion of a thermometer, 

 the whole to be covered in with a wooden case, to protect 

 it from dust and draughts, instead of the usual thin case 

 and water-bath. This method of securing a uniform 

 temperature is very satisfactory when no heat is generated 

 within the apparatus, but in the case of a resistance coil 

 and a thermometer placed in a hole filled with mercury 

 in the enclosing case, where the passage of the testing 

 current heats the wire, the thermometer would probably 

 " lag " considerably behind the wire ; and the chief effect 

 of the thick case would be to screen the thermometer 

 from the changes in temperature of the wire. 



The heat developed in a coil, and the rate at which the 

 temperature rises, are shortly considered, data being given 

 for calculating these quantities. It would be a great im- 

 provement, however, if in a subsequent edition a table 

 were given showing at a glance the maximum current 

 which can with safety be passed through the different coils 

 of resistance boxes wound with the sizes of wire ordinarily 

 used. Whether it would be possible to indicate this 

 quantity on the bo.xes of coils as sent out by the makers^ 

 is perhaps doubtful ; but if it could be done, it might 

 perhaps stay the hand of the too venturesome student, 

 who is continually trying to ruin any resistance boxes he 

 may be using by passing an excessive current. 



While the chapter on the Post Office and Dial forms 

 of Wheatstone's Bridge is very complete, and con- 

 tains a very useful table of the best resistances to 

 be used in the ratio arms of a Post Office Bridge, 

 that on the Slide Wire Bridge can hardly be said to be 

 so. The only form of Slide Wire Bridge at all fully 

 described and illustrated is of the ordinary design to 

 be found in elementary physical laboratories. Although 

 this is sufficient for teaching purposes, it is hardly suitable 



