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A WEEKLY ILLUSTRATED JOURNAL OF SCIENCE 



" To the solid ground 

 Of Nature trusts the mind which builds for a;^."— Word^wok r>l. 



THURSDAY, NOVEMBER 5, \i 



Revised and Edited by Silvanus 

 F.R.S. (London: Macmillan 



ELECTRICITY AND MAGNETISM. 

 Electricity and Magnetism. Translated from the French 

 of Amedee Guillemin, 

 P. Thompson, D.Sc. 

 and Co., 1891.) 

 ,nnHIS work is an English translation of M. Amedee 

 I J- Guillemin's popular treatise of electricity. We 

 ^are informed, in the preface, that the translation has been 

 m great part executed by Ivlr. Colman C. Starling and 

 'Prof. Walmsley, under the editorship of Dr. Silvanus P. 

 JThompson. It is a splendidly illustrated and beautifully 

 Igot-up book, designed, so the editor says, rather for the 

 table of the drawing-room than for the desk of the 

 student. 



We doubt whether, in fashionable drawing-rooms at 

 any rate, scientific curiosity exists to any great extent ; 

 but now that large houses are very frequently lighted 

 •ith electricity there may be a minority of people who 

 ire willing to spend any spare time left over from more 

 absorbing drawing-room occupations in learning some- 

 thing of how the light is produced and of other applica- j 

 tidiis of electricity. For such a public the present work i 

 seems exceedingly well adapted. It is popularly and ' 

 attractively written, so far as a translation from a j 

 foreign tongue, supplemented, and to some extent cor- | 

 reeled, by editorial paragraphs, can well be ; it is pro- 

 fusely illustrated, and comprehensive to an extent which j 

 has made the book almost too bulky for convenient 

 perusal. i 



-Still, the remnant of people by whom popular scientific \ 

 treatises such as this are welcomed, though numerous in | 

 itself, is, alas, only a very small minority of that great i 

 and influential section of the British public who are 

 brought directly into contact every hour of their lives 

 with the wonderful practical results of the progress of 

 science. The great majority converse through tele- 

 phones, consult their watches, and send telegrams, and 

 know no more than a Hottentot does how a telephone 

 .'acts, a watch goes, or a telegraph message is transmitted. 

 I NO. I 149, VOL. 45] 



The book is divided into two parts, dealing respectively 

 with phenomena and their laws, and practical applica- 

 tions ; or, speaking briefly, theory and practice. In the 

 theoretical part, magnetism is first treated, then electricity, 

 in the order statical electricity, electro-chemistry, and 

 electro-magnetism. In the practical part are comprised 

 telegraphy and telephony, electric lighting and trans- 

 mission of power, and a number of minor, but in them- 

 selves important, applications, such as clockwork-driving 

 and regulation, electricity in warfare, and electroplating. 

 Of the treatment of these subjects we can give here only 

 the merest sketch, noting as we do so a few points in 

 which the book seems to call for modification or im- 

 provement in a new edition. 



The theoretical part begins with a brief account of the 

 natural history of magnetism, then passes to a discussion 

 of the polar theory of magnetism, starting with the notion 

 of Thales that a magnet had a soul, and ending with the 

 experiments of Coulomb and their results. An excellent 

 description of Coulomb's torsion-balance experiments is 

 given, and then follow the methods devised by Coulomb 

 and Jamin for the determination of the distribution of 

 magnetism in magnets. It is hardly correct to say, as is 

 done on p. 33, that Coulomb's method " enabled him to 

 study the distribution of magnetism in magnets ; that is 

 to say, how the magnetism at the surface varies along the 

 magnet between one end and the other." Apart from 

 the objection that the field at any point external to the 

 surface of the bar depends really upon the whole distribu- 

 tion of magnetism, and not merely on that supposed to be 

 near the point, and the further objection (which also does 

 not seem to be stated here) that the vibrating needle itself 

 affects the magnetization of the magnet, it is (luite certain 

 that this method, like others devised for the same purpose, 

 cannot be made to give any definite information except 

 as to the surface-distribution of magnetism, which, as 

 Gauss showed, can be made to replace the magnet so far 

 as the external field is concerned. By none of these 

 methods can any information whatever be obtained as to 

 the actual magnetization of a bar of finite cross-section. 



It would have been well also if the editor had here 

 appended a note as to the essential inaccuracy of Jamin's 

 method " of placing on the point that we wish to study a 



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