December 14, 1905] NATURE 



'47 



of Faraday's ice-pail experiment — care should have 

 been taken to make the lines emanating from the 

 charged ball fall normally upon the vessel. The 

 properties of these lines are not dogmatically asserted, 

 but in general are derived, in the usual way, from 

 the inverse square law of force; exception must, 

 however, be made with respect to the lateral pressure 

 exerted by such tubes. In stating that the inverse 

 square law was experimentally verified first by 

 Coulomb the author seems to have forgotten 

 Cavendish, who, fully twelve years earlier, proved 

 that the index cannot differ from two by more than 

 1 50th part. 



We have alluded already to the diagrams; more 

 care than usual has been exercised in regard to these. 

 We are particularly attracted by one showing the 

 lines of force and induction of a horse-shoe magnet. 

 Compared with the usual paltry sketches of these 

 lines this is most excellent. The student ought to 

 be warned, however, that it represents rather an 

 artificial case, since the poles are taken as concen- 

 trated at points. In the absence of this warning 

 the student may be puzzled to account for the peculiar 

 configuration of the system of lines shown. Another 

 diagram which is now finding its way into text- 

 books is one (Fig. 354) showing the lines of electric 

 force due to a current. Much emphasis is usually 

 placed on the magnetic field, but the electric field is 

 almost entirely itmored. We are glad to see it now 

 beginning to take its proper place. It may be men- 

 tioned that if the conductors be taken as infinitely 

 deep, so as to reduce the problem to a two-dimensional 

 one, the lines of force are a family of rectangular 

 hyperbolae, while the equipotential lines are the 

 orthotomic hyperbola?. 



Several omissions and errors require attention. 

 In the chapter on mechanics there is no definition 

 of mass — we are not even told that it is the quantity 

 of matter in a body. It is erroneous to state that 

 electrification and electric currents are forms of 

 energy (p. 22). A hollow soft iron cylinder does not 

 act as a perfect screen to magnetic force for points 

 inside it (p. 65). The proof of the formula for the 

 ballistic galvanometer (p. 282) is imperfect, since it 

 assumes that the current is constant while it flows ; 

 win rcas it essentially is never so in cases for which 

 this kind of galvanometer is used. A verv little 

 change in the proof will put this right. In the 

 formula for simple pendulum or suspended coil the 

 time period should not be written with sin 0/0 in the 

 denominator, since when so written the idea is con- 

 veyed that this is the proper form when the difference 

 between sin and is too large to be neglected. In 

 calculating the temperature of a wire when heated 

 by a current the emissivity should not be taken as 

 a constant, for Messrs. Ayrton and Kilgour confirmed 

 Peclet's proof that it depends on the radius; for very 

 thin wires the values go up to many times that 

 quoted, except, of course, in a vacuum. Kelvin's 

 proof of the existence of an E.M.F. distributed in a 

 circuit of two metals parts of which are at different 

 temperatures depended on the first law of thermo- 

 dynamics, and not upon the properties of a Carnot j 

 NO. 1885, VOL. J3] 



cycle (p. 374). The definition of units is antiquated; 

 those described (p. 515) are now obsolete. On 

 p. 531, in connection with displacement currents the 

 word displacement is used on adjacent lines in two 

 senses, with consequent confusion to the meaning. 

 The treatment of the calculation of the propagation of 

 electrodynamic effects (p. 534) which is professedly 

 applicable to the case when the exciting current is 

 travelling along a wire is inapplicable to this case. 

 The display of mathematics in this calculation will 

 convey the erroneous impression of a thorough in- 

 vestigation. The result must be disastrous to a 

 student who is feeling his way toward a knowledge 

 of the subtleties of line-integration round a closed 

 curve. The error arises in part from forgetting that 

 the magnetic induction varies in the direction y as 

 well as in the direction x. Everything is, we believe,, 

 put right if the conductor be taken as an infinite 

 plane sheet; the variation which is omitted is in such 

 a case zero. 



These few errors are the more unfortunate since 

 we think that the book will prove a very useful one. 

 We frankly think that it has been attempted to put 

 too much into small compass ; most sections would 

 be improved by amplification in explanation of prin- 

 ciple at the sacrifice of detail. A little excision when 

 this edition is exhausted, a little more attention to 

 logical order and to the development of principles — 

 such suggestions are worth attending to, for the 

 book has the making of a very useful volume. 



BUN SEN'S COLLECTED WORKS. 

 Gesammelte Abhandlungen von Robert Bunsen. 

 Edited by Wilhelm Ostwald and Max Bodenstein. 

 Vol. i., pp. cxxvi + 535; vol. ii., pp. vi + 660; vol. iii. r 

 pp. vi + 637. (Leipzig: Engelmann ; London: 

 Williams and Norgate, 1904.) Price 2/. 10s. net. 



THE appreciative and critical notices of Bunsen 

 and his work which appeared shortly after his 

 death hardly leave room for a review of the volumes 

 before us. In the Chemical Society memorial lecture, 

 which is justly given the place of honour in the pre- 

 fatory part of the first volume, Sir Henry Roscoe has 

 given a comprehensive survey of Bunsen 's work, and 

 has described the personality of the man in such a 

 way as to earn the gratitude of all old Heidelberg 

 students. ' 



In these three stately volumes we have a complete 

 collection of Bunsen's contributions to science and a 

 book that will form part of the permanent literature 

 of chemistry. It is, indeed, a most striking fact that 

 all Bunsen's writings are in their nature permanent 

 scientific literature, a fact that well deserves ponder- 

 ing at the present time. He made some mistakes, 

 he advanced some conclusions now untenable, but his 

 writings are of faithful observations, careful experi- 

 ments, laboratory methods. Of speculative theory 

 there is nothing, and of strictly polemical writing also 

 nothing. The books that are included in his writings 

 are accounts of methods of doing things that he him- 



1 An account of Bunsen's scientific woik was given by Sir Henry Roscoe 

 in Nature of April 28, 1881 (vol. xxiii. p. 597), as a contribution to our 

 series of " Scientific Worthies.' — Editor 



