428 Lord Rayleigli. 



Maxwell, and Stokes whom lie claimed as his own special 

 mentor, their author stands at the head of the general 

 theoretical physics of! his age. 



The second edition of the Theory of Sound, revised and 

 enlarged, appeared in 1896 extended to nearly twice the 

 original size; it thus became even more emphatically a treatise 

 on the general dynamical principles regulating vibrational 

 and undulatory phenomena, developed indeed with reference 

 mainly to the simplest and most tractable case, that of 

 pressural waves in air, but in close touch with the more 

 complex problems of optics and electricity. Thus a special 

 chapter on electric waves expounded very concisely the 

 dynamical principles of electric resonance initiated mainly 

 by Maxwell, which have become essential to refined electric 

 technology in all its branches; though more than twenty 

 years old, it. covers the subject in a manner so concise and 

 complete that at the present day hardly anything but 

 additional and even more wonderful practical illustrations 

 need be added. 



Everywhere fresh suggestions occur. Thus, for example, 

 one of the additions is an exposition of the analysis employed 

 by Kirchhoffto explain the falloE velocity when sound travels 

 in narrow tubes or channels, which was traced mainly to the 

 absorption of the reversible heat of compression in the 

 waves by the walls o£ the tube. But Lord Rayleigh goes on 

 incidentally (§ 351) to explain a far more important feature, 

 the degradation of the energy of the waves that is involved; 

 and the absorption by a curtain or other porous medium of 

 sound that is incident on it thus receives its precise and most 

 suggestive explanation, developable on a quantitative basis 

 and with application to practical problems relating to the 

 prevention of echo and reverberation. 



Lord Rayleigh was born in 1842 ; he graduated at Cam- 

 bridge in Jan. 1865 as Senior Wranoler and First Smith's 

 Prizeman, sending in papers to the examiners which revealed 

 a lucidity and precision that foreshadowed one side of his 

 future achievement. He succeeded his father in the peerage 



