266 PETER GUTHRIE TAIT 



write an elementary article, he does it admirably. Witness his Notes on Hydrodynamics, 

 especially that entitled On Waves. 



Before that article appeared, an article as comprehensive as it is lucid, the subject 

 was almost a forbidden one even to the best student, unless he were qualified to attack 

 the formidable works of Laplace and Airy, or the still more formidable memoirs of 

 Cauchy and Poisson. Here he finds at least the main points of this beautiful theory, 

 disencumbered of all unnecessary complications, and put in a form intelligible to all 

 who have acquired any right to meddle with it. It is quite impossible to tell how much 

 real good may be done by even one article like this. Would there were more such ! 

 There are few, even of the most gifted men, who do not occasionally require extraneous 

 assistance after the earlier stages of their progress : all are the better for it, even in their 

 maturer years. 



The contents of these two volumes consist mainly, almost exclusively, of papers 

 connected with the Undiilatory Theory of Light or with Hydrodynamics. On the former 

 subject at least, Stokes stands, without a living rival, the great authority. From the 

 Aberration of Light, the Constitution of the Luminiferous Ether, the full explanation of 

 the singular difficulties presented by Newton's Rings, to the grand theoretical and 

 experimental treatise on the Dynamical Theory of Diffraction, we have a series of 

 contributions to this branch of optics which, even allowing for improved modern 

 surroundings, will bear comparison with the very best work of Newton, Huyghens, 

 Young, or Fresnel in the same department. 



Specially remarkable among the Hydrodynamical papers is that on Oscillatory 

 Waves, to which a very important addition has been made in the reprint. The 

 investigation of the " profile " of such a wave is here carried to a degree of approximation 

 never before attempted. 



Besides these classes of papers we have the very valuable treatise on Friction of 

 Fluids in Motion, and on the Equilibrium and Motion of Elastic Solids. This was 

 Stokes" early masterpiece, and it may truly be said to have revolutionized our knowledge 

 on the subjects it treats. To mention only one point, though an exceedingly important 

 one, it was here that for the first time was clearly shown the error of assuming any 

 necessary relation between the rigidity and the compressibility of an elastic solid, such 

 as had been arrived at from various points of view by the great Continental 

 mathematicians of the earlier part of the present century. 



Of the few purely mathematical papers in the present volumes the most important 

 is the well-known examination of the Critical Values of the Sums of Periodic Series, 

 a subject constantly forced on the physicist whenever he has to treat a case of 

 discontinuity.... 



Tait contributed to Nature three reviews on Stokes' Burnett Lectures, 

 which were delivered in Aberdeen in three Courses and were published in 

 three corresponding volumes about a year apart. The review of the First 

 Course, On the Nature of Light, appeared on April 10, 1884 (Vol. xxix). 

 The Second Course, On Light as a Means of Investigation, was reviewed on 

 August 20, 1885 (Vol. xxxn). The following extracts are of special interest: 



