February ii, 1909J 



NA TURE 



425 



densing the manifold discoveries of recent years into 

 small compass without sacrifice of accuracy. But he 

 would have produced a more readable, and, we think, 

 more effective book, had he ruthlessly cut out half his 

 information, and expanded the other half so as to 

 supply a series of more carefully graded explanations. 

 .\ youth who has already made a hobby of electrical- 

 instrument making or who has studied the subject 

 successfully at school might read " Electricity for 

 ^"<>ung People " with interest, and in that case he 

 wiiuld certainly read it with profit. 



(4) In the fourth volume of the series, Mr. Jenks had 

 an easier task, since " Photography for Young 

 People " appeals directly to a favourite pursuit. There 

 is a good chance of success for any book of moderate 

 [jrice which tells a boy with sufficient clearness the 

 niithods by which he can succeed in his hobby. In 

 llii^ book the young photographer will find good prac- 

 tical instructions, and a particularly clear exposition of 

 the principles of the art he is striving to master. The 

 author is at home alike when dealing with the begin- 

 nings of photography and when putting the latest 

 discoveries within reach of the young amateur. Tech- 

 nical terms are properly treated, i.e. they are not 

 evaded, but used after explanations have been given 

 in simple language. The acquisition of such terms 

 is enjoyed by a boy, and is good for him provided they 

 are made to become part of his mental possessions — 

 tools in his mental workshop. In each of these 

 volumes a very fair standard is reached as regards 

 illustrations, print, and binding. A plea may be urged 

 for yet more copious illustrations in such books, as 

 the youthful reader is greatly helped thereby. Both 

 (3) and (4) are well indexed. G. F. D. 



VHYSICAL ACOUSTICS. 

 (i) .4 Text-book of Sound. By Prof. E. H. Barton. 

 Pp. xvi-t-687 ; illustrations. (London: Macmillan 

 and Co., Ltd., 1908.) Price los. net. 

 (2) Traite de Physique. By O. D. Chwolson. 

 Translated by E. Davaux. Tome i., fascicule iv. 

 .Acoustique. Pp. vii + 873-1092. (Paris : .\. Her- 

 mann, igo8.) Price 8 francs. 

 (1) T3ROB.\BLY no branch of physics is so poorly 

 -L represented by text-books as that of sound. 

 Between very elementary volumes and Lord Ravleigh's 

 masterly treatise very little exists. The former are 

 too trivial, while the latter is far too severe for the 

 first or second year senior undergraduate. For this 

 reason, amongst others, the present volume will be 

 received gladly bv both teacher and student, for it 

 very adequately fills the gap in our expositional 

 literature. 



What, then, are llie main characteristics of this 

 book which confer superiority upon it? In the first 

 place, the author does not hesitate to employ the 

 eleinents of the calculus, although in many cases 

 geometrical proofs are given as well. We think the 

 day is now gone in which it was supposed that a 

 student's undergraduate work could be carried on 

 without reference to the calculus. We know that 

 university regulations have in some cases encouraged 

 this belief; but teachers have for a long time ignored 



NO. 2050, VOL. 79] 



these restrictions and have freely employed the 

 calculus in their demonstrations. We hope that the 

 time may come when mathematicians will see their 

 way to give an adequate introduction to such methods 

 in the first collegiate year. It is possible that some 

 matters which are dear to them will need to be post- 

 poned until later in order that this may be done. 

 The attempt is made, and satisfactorily so, in some 

 schools ; we hope that this practice will become 

 universal. It is true that in some cases an exceed- 

 ingly quick and convincing proof of a theorem can 

 be obtained by geometrical inethods ; but, on the other 

 hand, the present writer could lay his finger on pages 

 of proof, partly algebraic, partly graphical, which 

 could all be condensed into a few lines, and which 

 have caused endless bother to the students with whom 

 he has come in contact. Even in the book before us 

 the graphical parts are not those which are clearest, 

 though we have nothing but praise for the thorough 

 way in which those parts are dealt with. 



The second main characteristic is the close connec- 

 tion, maintained throughout, between theory and 

 experiment. A treatise on sound is bound to be some- 

 what mathematical ; but the author never misses a 

 chance of introducing an experimental illustration or 

 an account of some experimental verification of a 

 theorem proved. 



After a short preliminary survey the book continues 

 with a somewhat long mathematical account of the 

 kincmatical and dvnamical bases of the subject (in- 

 cluding a chapter on elasticity). It is, perhaps, in 

 this part that a curtailment might have been made. 

 The elastic properties of bodies are now usually con- 

 sidered under the head of properties of matter. (By 

 the way, is not the method for calculating the velocity 

 of sound in a gas which starts by superposing an 

 equal but opposite velocity due to Rankine? The 

 author seems to imply that it is Rayleigh's method.) 

 We regret that the part devoted both to the theoretical 

 and experimental side of diffraction should be so short. 

 Dr. Barton probably considers that this should be left 

 to be treated in a text-book on light. 



In the third place, we commend this book because 

 it rings true to the spirit of research. The author has 

 himself contributed in some degree to our knowledge 

 of the subject, and he is abreast of the most recent 

 work that has been done in connection with it. This 

 is very notably the case in the laige section which 

 deals with musical instruments. Dr. Barton is 

 specially qualified to deal with this side of the subject. 

 The result is that we find here a compendium on the 

 physical side of the qualities of musical instruments 

 such as we believe cannot be found elsewhere. 



Of recent work considered, mention may be made 

 of Lord Rayleigh's work on the perception of sound 

 direction, recent considerations in connection with the 

 piessure of radiation, modern work on combination 

 tones (no mention is made, however, of Barrett and 

 Bolas's work on this subject), and the work of Sabine 

 and of Marage on architectural acoustics. The last 

 item is one in connection with which very little is 

 definitely known, and to which research might very 

 well be directed. 



