122 



NATURE 



[June 9, 1898 



the best known being the striations which are always 

 seen in a Kundt's tube, and which are shown to be due 

 to the tendency of solid particles to arrange themselves 

 in chains perpendicular to the lines of alternating flow. 

 An investigation of reflection at a corrugated surface 

 follows, next comes a description of some experiments 

 on diffraction of sound. 



A general account of the mode of maintenance of the 

 vibrations of a flute organ-pipe is then given, and 

 attention is called to the fact that the note of the pipe 

 when sounded is higher than the note to which it would 

 resound, and that the difference increases with the wind 

 pressure. The mutual influence of organ-pipes mounted 

 side by side is considered ; it has been shown how this 

 influence militates against the successful application to 

 pipes of Scheibler's method of determining absolute 

 pitch. The maintenance of vibrations by increasing the 

 pressure at a node at a time of maximum pressure and 

 decreasing it at a time of minimum pressure by the 

 introduction and removal of air or of heat is considered. 

 (The student will find it a profitable mental exercise to 

 satisfy himself that this mode of maintenance is con- 

 sistent with the general principle that the force should 

 be applied when the system passes through its equi- 

 librium position ; he may also note the analogy to the 

 maintenance of the oscillations of a galvanometer needle 

 by a small current suitably controlled by a reversing 

 key). If, on the other hand, the moments of the most 

 rapid addition and subtraction of heat are those of most 

 rapid change of pressure, it is shown that the vibration 

 is neither maintained nor damped, the effect being 

 concentrated upon the period. It may be remarked 

 that the passage from Newton's theory of sound to 

 Laplace's, or vice versd, in calculating the pitch of a 

 pipe is a case exactly in point. Among the more 

 important applications of maintenance by heat, singing 

 flames and Rijke's sounding tubes are treated, also the 

 sounds sometimes heard when a bulb has just been 

 blown at the end of a glass tube. The maintained 

 vibration of mercury contained in a U-tube, one end of 

 which is connected with a heated bulb, is a visible 

 example of the latter phenomenon, and the principle has 

 been successfully applied to small hot-air motors. A 

 short account of the conditions of maintenance in reed 

 instruments is also given. 



Under the head of fluid friction, Kirchoffs investiga- 

 tion of the effects of viscosity and heat-conduction 

 upon the propagation of sound finds a place, and the 

 behaviour of very narrow tubes towards sound is applied 

 to the question of reflection at a porous wall. The 

 theory of the vortices observed by Dvorak in Kundt's 

 tubes is also investigated. 



Four new chapters complete the book. The first deals 

 with liquid waves under gravity and cohesion ; in it are 

 treated, among other matters, the determinations of surface 

 tension by the measurement of ripples and by observations 

 on the vibrations of a liquid cylinder, the importance of the 

 latter method in permitting the examination of a newly- 

 formed surface being pointed out. The instability of a 

 hquid jet, the behaviour of drops in collision, and the 

 vibrations of detached drops are also considered. The 

 next chapter, on vortex motion, gives an investigation of 

 the instability of stratified motion in a fluid, and its 

 NO. 1493, VOL. 58] 



application to the theory of sensitive flames and smoke- 

 jets. Bird-calls and aeolian tones are also shortly 

 treated, some considerations as to pitch being deduced 

 from the principle of dynamical similarity. A brief account 

 of the propagation of vibrations in elastic solids follows, 

 and the last chapter deals with facts and theories of 

 audition. In it the author's experiments on the minimum 

 amplitude of sound waves consistent with audibility are 

 described, a discussion of Ohm's law and its exceptions 

 is given, and, by the application of dynamical principles 

 to the internal vibrators which on Helmholtz's theory form 

 the analysing mechanism of the ear, the bearing of the 

 degree of damping in these vibrators on the origin of 

 dissonance, on the possibility of accurately judging 

 pitch, and on the remarkable results of Kohlrausch as to 

 the exceedingly small total number of vibrations requisite 

 for the appreciation of a definite pitch, is explained. 

 Finally, the conflicting views which have been held as to 

 combinational tones, the perception by the ear of the 

 phase relationship of two tones, and the characteristics 

 of vowel sounds are discussed. 



In Nature of December 12, 1878, Prof. Helmholtz, 

 after suggesting some of the above problems, wrote of 

 the first edition of this book : " Lord Rayleigh certainly 

 deserves the thanks of all physicists and students of 

 physics ; he has rendered them a great service by what 

 he has done hitherto. But I believe I am speaking in 

 the name of all of them if I express ihe hope, that the 

 difficulties of that which yet remains will incite him to 

 crown his work by completing it." This has now been 

 done, but the only voice which could without impertinence 

 utter praise is, alas, silent. L. R. W. 



HAWKS AND HAWKING. 

 Hints on the Management of Hawks (Second Edition) ; 

 to which is added Practical Falconry Chapters, 

 Historical and Descriptrve. By J. E. Harting. 8vo. 

 Pp. viii -I- 268, illustrated. (London : H. Cox, 1898.) 



MR. HARTING is such an authority on the art of 

 hawking, and is, furthermore, such an excellent 

 field naturalist, that it was only to be expected his 

 volume on this branch of sport would reach a second 

 edition. But, as the author states in his preface, the 

 additions to the new edition, both as regards letter-press 

 and illustrations, are so extensive as almost to give it a 

 claim to rank as a new work. 



From all points of view, management, rearing, training, 

 and use in the field, as well as regards their natural 

 history, Mr. Harting appears to have furnished all that 

 there is to be told concerning hawks and hawking ; and if 

 the votaries of this sport are not satisfied with his efforts, 

 they must indeed be hard to please. Some of the most in- 

 teresting chapters in the volume are those relating to the 

 now obsolete kite-hawking and heron-hawking ; the one 

 of which has ceased to exist from the practical extinction 

 of the quarry, and the other from the altered physical 

 conditions of the country. In all portions of his subject 

 the author owes much to the artist, some of the illustra- 

 tions being really exquisite, especially those from the 

 pencil and brush of Mr. Lodge. What, for instance, can 

 be more striking than the contrast between the figure of 



