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XXII. Notices respecting New Books. 



A Treatise on Electricity and Magnetism. By E. Mascart and 

 J. JouBEET. Translated by E. Atkinson, Ph.D., F.O.S. 



Vol. II. Methods of Measurement and Applications. 



TT is hardly necessary to say that MM. Mascart and Joubert 

 ^ have, in publishing this treatise, done a very great service to 

 Electrical Students. Those who are not acquainted with the work 

 will obtain a very good idea of its nature i£ they imagine that a 

 professor well acquainted with Clerk-Maxwell's work has here 

 tried to give to students equipped only with the usual knowledge 

 of the Differential and Integral Calculus, not only a clear under- 

 standing of Maxwell, but a clear knowledge of w^hat has been done 

 in developing the quantitative study of electricity since Maxwell's 

 time. This second volume is likely to be of very great use to expe- 

 rimenters and electrical engineers. The treatment of the subject 

 is very complete ; indeed it strikes a person who reads steadily 

 through the book that there is somewhat too much detail ; but it 

 is very probable that when the same reader uses the book after- 

 wards as a book of reference, he may feel very thankful for the 

 elaborate working out of corrections which are of so much import- 

 ance in the laboratory. We are not now speaking of such details 

 as the proof of the law of torsion in a cylindric wire (pages 55-6), 

 because such matter seems to us as unnecessary as the proof of one 

 of Euclid's propositions in such a book. Again, there are certain 

 refinements in correcJ;ion which seem to us unnecessary ; for ex- 

 ample, the length of one spire in the winding of a coil may usually 

 be taken as equal to the circumference of the axial cylinder without 

 the introduction of a correcting term. It is, however, quite pro- 

 bable that other readers may not agree with us here ; whereas as 

 to the obvious great merits of the book, and even to such a merit 

 in the translation as the creation of an index (although the index 

 might be advantageously amplified), there can be no difference of 

 opinion. 



The work is divided into four parts : — I. Methods of Measure- 

 ment, 165 pages, II. Electrical Measurements, 400 pages. 

 III. Magnetic Measurements, 111 pages. IV. Complement, 

 88 pages. 



We shall say a few words about Part I., for the purpose of 

 giving an idea of the general method of treatment adopted by the 

 authors and translator. 



Part I. begins with corrections for temperature in measuring 

 length ; corrections for the air in weighing ; and 13 pages are de- 

 voted to a description of various methods of measuring angles and 

 their limits of accuracy, the methods described being all optical. 

 The second chapter is devoted to a study of vibrations ; vibrations 

 damped when the resistance is proportional to the velocity, and 

 also when it is proportional to the square of the velocity. This is 

 a chapter which will be found very useful in the laboratory ; and 



