232 Professor Joseiih Larmor [May 1, 



more lectures, which transformed optics for the time from an affair of 

 abstract mathematical equations into a subject of direct physical con- 

 templation, in close touch and analogy with the objective manifesta- 

 tions of ordinary dynamics. 



In the preface to the authoritative edition of 1904, which in the 

 twenty years' interval had grown to be a volume of some 700 pages 

 octavo, Lord Kelvin in fact describes the object of the course of 

 lectures as follows : " I chose as subject the Wave Theory of Light 

 with the intention of accentuating its failures, rather than of setting 

 forth to junior students the admirable success with which this beautiful 

 theory had explained all that was known of light before the time of 

 Fresnel and Thomas Young, and had produced floods of new know- 

 ledge, splendidly enriching the whole domain of physical science. 

 My audience was to consist of professorial fellow-students in physical 

 science ; and from the beginning I felt that our meetings were to be 

 conferences of coefficients * in endeavours to advance science, rather 

 than teachings of my comrades by myself. I spoke with absolute 

 freedom, and had never the slightest fear of undermining their perfect 

 faith in ether and its light-giving waves ; by anything I could tell 

 them of the imperfections of our mathematics ; of the insufficiency or 

 faultiness of our views regarding the dynamical qualities of ether ; 

 and of the overwhelmingly great difficulty of finding a field of action 

 for ether among the atoms of ponderable matter. We all felt that 

 difficulties were to be faced, and not to be evaded ; were to be taken 

 to heart, -with the UoiJe of solvi/ng them if jiossible ; but, at all events, 

 with the certain assurance that there is an explanation of every diffi- 

 culty though we may never succeed in finding it." 



He goes on to say that he had now, in 1904, virtually got to the 

 bottom of the difficulties of 1884. He thinks, too, that in the wider 

 field of sethereal phenomena everytJimg non-rnagnetic can be explained 

 "without going beyond the elastic solid theory," but nothing magnetic. 

 "The so-called electro-magnetic theory of light has not helped us 

 hitherto ; but the grand object is fully before us of finding compre- 

 hensive dynamics of ether, electricity, and ponderable matter, which 

 shall include electrostatic force, magnetostatic force, electro-magnetism, 

 electro-chemistry, and the wave theory of light." 



His purely scientific activity from 1884 onwards hinged largely 

 on the production of the definitive edition of these lectures, which, 

 in terms of the remarks just quoted, had raised up in front of him all 

 the difficulties in modern optical and general ethereal theory. The 

 resulting volume, with its numerous insertions, including most of pp. 

 280-468, and the twelve Appendices occupying pp. 648-700, may 

 take rank in fact as virtually Volume IV. of the ' Mathematical and 

 Physical Papers.' Among the vast array of new and recent material 

 collected into the volume there may be mentioned the following : 



* In the literal sense of the term. 



