NATURE 



[May i6, 1907 



at the same time as acting at the point of contact 

 between the disc and the surface. 



(6) In the " Piactical Physics " of Messrs. Bower 

 and Satterly we have a course intended for matricu- 

 l.ited students. No previous knowledge of experi- 

 mental physics is assumed, however, and hence the 

 handboolc is a complete elementary manual of the 

 subject. Great pains have evidently been taken to 

 secure efficiency, and the result is a text-book which 

 merits great praise. Both the writers have had con- 

 siderable experience in practical work, and, moreover, 

 have the ability to impart the results of this experi- 

 ence to others. The volume is profusely illustrated 

 with sketches, which will pro%'e of great use to 

 teachers who are obliged to make their own 

 apparatus. Most of the experiments are intended to 

 be performed in a properly equipped laboratory; 

 certain of them arc designed to be performed at home. 

 The latter have been arranged so as to keep the cost 

 of performance low, but at the same time merely 

 trifling experiments have been avoided. These ex- 

 periments form part of the complete course, and are 

 meant to be done in a laboratory, if not at home. 



(7) In spite of the considerable merit of the pre- 

 ceding manuals, we turn from them to Dr. Jude's 

 elementary treatise and peruse it with some sense 

 of exhilaration. It is only a school book, contain- 

 ing " all of the subject that is required for the London 

 University Matriculation," though not written to the 

 syllabus of any examination ; but from first to last 

 there is an originality of treatment which makes it 

 interesting reading even to one who is hlase in the 

 reading of text-books. Our only doubt is whether 

 it is not too thorough for such examinations as that 

 named ; a wise teacher will know, however, how to 

 benefit by it himself, and at the same time to temper 

 it to the more junior boys without sacrificing the 

 thoroughness. According to its subtitle, it is based 

 on " potential and potential-gradient," notions which 

 even university students sometimes find it hard to 

 grasp. The fallacy of the old theory of " free and 

 bound " charges is exposed, and this exposure is 

 made much more effective than is customary. It is 

 shown that when a conductor is under electric induc- 

 tion, the amount of electricity which runs out of the 

 conductor on earthing is not in general equal to that 

 which resided beyond the neutral line before the earth 

 connec^ion was made. In the case of a sphere under 

 the action of a point-charge placed at a distance of 

 four times the radius from the centre, the so-called 

 ■" bound " charge is less than one-fifth of the induced 

 •charge when the sphere is earthed. A matriculation 

 pupil will not understand the mathematical quotations 

 in respect to this point, but these quotations will 

 serve to keep many a teacher on the right path. 

 This example indicates the thoroughness character- 

 istic of the volume. The diagrams are numerous, 

 and, in general, are good, but it is certainly with 

 Ttgret, and also with some surprise, that we see 

 certain familiar lines-of-force diagrams doing duty 

 once more. A moment's reflection should persuade 

 anyone that a diaper pattern between two north poles 

 (p. 206) hardly does justice to the lines as pourtrayed 

 by iron-filings, imperfect though these are. Still less 



NO. 1959, VOL. 76] 



does it do justice to the true lines of force between 

 two such poles. The figure for two opposite poles 

 (Fig. 94j should also be replaced by a much more 

 satisfactory one. We do not wish to conclude the 

 notice of the book by an adverse criticism, however 

 slight. It has given us great pleasure to read 

 thiough it, and we hope that this pleasure will be 

 felt by very many more. 



(8) The collection of mechanics problems made 

 by Mr. Sanborn is a second edition of a book pre- 

 pared for engineering students. The aim has been 

 to present many practical problems, together with 

 brief definitions and solutions of typical problems, to 

 help the student to follow George .Stephenson's 

 advice to his son Robert : Learn for yourself, think 

 for yourself, make yourself master of principles. 

 It is illustrated with process-work cuts in the new 

 manner, presumably with the object of adding interest 

 to a mere collection of problems. Whenever these 

 cuts illustrate a ddinite point, their inclusion acquires 

 a real value. In some cases the moral is somewhat 

 hazy. The frontispiece of an engine belching black 

 smoke on an up-grade on the Pennsylvania Railroad 

 at Tyrone seems somewhat superfluous, especially as 

 the camera, having seized the wrong perspective, has 

 given the lines a down-grade rather than an up-grade 

 appearance. In other cases, wherr, for example, it 

 is a dipper dredge which is depicted in full working 

 Older, the picture is necessary to the proper under- 

 standing of the problem on the opposite page. There 

 is a novelty about the choice of problems which we 

 verv much appreciate. The utility of the book would 

 be enhanced if more of these problems were worked 

 out in detail. With regard to provision of answers, a 

 middle ground has been taken in giving them to 

 about half the questions. The answer to a problem 

 is not the principal thing from the standpoint ot 

 education, though it of course becomes very important 

 when it forms the basis of a monetary transfer. The 

 one feature of the book which wc fail completely to 

 understand is thf order in which the questions are 

 arranged — work, force, motion. Is it possible that it 

 is intended that the exercises should be performed 

 backwards ? 



(q) " .\ First Course of Physics," by Drs. Millikan 

 and Gale, " has grown out of the actual needs of the 

 elementary work in Physics in the University of 

 Chicago, particularly in the University High School." 

 The aim has been to give " a simple and immediate 

 presentation, in language which the student already 

 understands, of the hows and whys of the physical 

 world in which he lives." It must not be understood 

 from this quotation that we have here merely a com- 

 pilation for the amateur reader; the volume is a 

 genuine text-book for schools. We think that in the 

 choice of matter and in its treatment the authors 

 have been successful. Not the least valuable feature 

 is the large number of excellent portraits of physicists, 

 old and new, from .\ristotle to Galileo, Maxwell, and 

 J J. Thomson ; these will help to stimulate the 

 budding genius. In the section on image formation 

 the method of wave-curvature has been adopted. We 

 agree that in the elementary treatment of images 

 there is advantage in this method ; at the same time, 



