THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[SIXTH SERIES.] 



AUGUST 1901. 



XII. On Ether and Gravitational Matter through Infinite 

 Space. By Lord Kelvin*. 



[This is an amplification of Lecture XVI., Baltimore, 

 Oct. 15, 1884, now being prepared for print in a volume on 

 Molecular Dynamics and the Wave Theory of Light, which I 

 hope may be published within a year from the present time.] 



Note on the Possible Density of the Luminiferous 

 Medium, and on the Mechanical Value of a Cubic 

 Mile ft of Sunlight. 

 [From Edin. Royal Soc. Trans, vol. xxi. Part I. May, 1854 ; Phil. Map-. 



ix. 1854; ComptesEendus, xxxix. Sept. 1854; Art. lxvii. of Math, and 



Phys. Papers.] 



§ 1. rilHAT there must be a medium forming a continuous 

 JL material communication throughout space to the 

 remotest visible body is a fundamental assumption in the 

 imdulatory Theory of Light. Whether or not this medium 

 is (as appears § to me most probable) a continuation of our 



* Communicated by the Author. 



t [Note of Dec. 22, 1892. The brain-wasting- perversity of the insular 

 inertia which still condemns British Engineers to reckonings of miles and 

 yards and feet and inches and grains and pounds and ounces and acres is 

 curiously illustrated by the title and numerical results of this article as 

 originally published.] 



X [Oct. 13, 1899. In the present reproduction, as part of my Lee. xvi. 

 of Baltimore, 1884, I suggest cubic kilometre instead of " cubic mile" in 

 the title, and use the French metrical system exclusively in the article.] 



§ [Oct. 13, 1899. — Not so now. I did not in 1854 know the kinetic 

 theory of gases.] 



Phil. Mag. S. 6. Vol. 2. No. 8. Aug. 1901. M 





