THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE 



[SIXTH SERIES.] 



JULY 1901. 



I. Nineteenth Century Clouds over the Dynamical Theory of 

 Heat and Light *. By The Eight. Hon. Lord Kelvin, 

 G.C.V.O., D.C.L., LL.L)., F.R.S., M.R.I. f. 



[In the present article, the substance of the lecture is 

 reproduced — with large additions, in which work com- 

 menced at the beginning of last year and continued after 

 the lecture, during thirteen months up to the present time, 

 is described — with results confirming the conclusions and 

 largely extending the illustrations which were given in the 

 lecture. I desire to take this opportunity of expressing my 

 obligations to Mr. William Anderson, my secretary and 

 assistant, for the mathematical tact and skill, the accuracy 

 of geometrical drawing, and the unfailingly faithful per- 

 severance in the long-continued and varied series of drawings 

 and algebraic and arithmetical calculations, explained in the 

 following pages. The whole of this work, involving the 

 determination of results due to more than five thousand 

 individual impacts, has been performed by Mr. Anderson. — 

 K., Feb. 2, 1901.] 



§ 1. rilHE beauty and clearness of the dynamical theory, 



JL which asserts heat and light to be modes of 



motion, is at present obscured by two clouds. I. The first 



came into existence with the undulatory theory of light, and 



* Lecture delivered at the Royal Institution of Great Britain, on 

 Friday, April 27, 1900. 



f Communicated by the Author. 

 Phil. Mag. S. 6. Vol. 2. No. 7. July 1901. B 



