Intelligence and Miscellaneous Articles. 387 



equations and integrate them, enabled a variety of results to be 

 explained which altogether puzzled the older investigators, and 

 would probably have remained a mystery to this day had it not 

 been for the industry and skill of the despised mathematicians. 



If the anonymous reviewer will read through chapters XI., XiT., 

 and xv., he will find that the physical constitution of the tether 

 according to Green's theory, and also according to Lord Kelvin's 

 modification of Lord Eayleigh's theory, is fully explained ; and 

 that the principal mathematical developments are given, and dis- 

 cussed in relation to experimental phenomena. What more can 

 he want? 



The next stage in the history of the subject consists in the 

 attempt to account for dispersion and absorption by means of the 

 mutual reaction between aether aud matter. The physical idea 

 which lies at the root of such theories is so exceedingly simple, that 

 it would be difficult for a person afflicted with the most exuberant 

 verbosity to write more than a page or two of general talk upon 

 the subject. The real difficulty lies in attempting to express this 

 idea in a mathematical form, as will be seen by consulting the 

 somewhat voluminous German literature upon the subject. I 

 decided, after some consideration, to confine myself to the theories 

 of Lord Kelvin and von Helmholtz. The former theory is espe- 

 cially valuable, because it enables us to construct a mechanical 

 model of a medium which produces anomalous dispersion ; whilst 

 the latter theory, besides giving a partial explanation of selective 

 reflexion, enables us to place Cauchy's formulas for metallic reflexion 

 on a dynamical basis. 



In conclusion, I will give an example which shows how necessary 

 it is to cover up the nakedness of the physical skeleton with 

 mathematical clothing. Many years ago the hypothesis was for- 

 mulated (by Lord Kelvin, I believe) that magnetic force was the 

 effect of something in the nature of rotation. So far so good ; but 

 in the absence of the fructifying influence of mathematical analysis 

 the idea would have remained as barren as a seed lying in the 

 desert. There is no a priori reason for supposing that rotation of 

 the medium would produce rotation of the plane of polarization of 

 eethereal waves ; for it might equally well have happened that it 

 would change a plane-polarized wave into a single elliptically pola- 

 rized wave. But, thanks to mathematical analysis, we now know 

 that rotation of the plane of polarization is a necessary consequence 

 of rotation of the medium. 



The reviewer has finally come forward as an authority on style. 

 How far he is competent to assume that character may be judged 

 from the following quotations : — " But, as the author in his preface 

 says " (then follows a passage from my book concluding with a full 

 stop). " This last, by the way, is one of the extraordinary state- 

 ments." " The entirely admirable text-book of Mr. Preston." 

 I am, Gentlemen, 



Your obedient Servant, 



A. B. Basset. 



