XED. 



THE 

 LONDON, EDINBURQH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[SIXTH SERIES.] 



SEPTEMBER 1905, 



XXXYI. On the Statistical Kinetic Equilibrium of Etker in 

 Ponderable Matter, at any Temperature. By Lord Kelvin"*. 



§ 1. /CONSIDER first the simplest possible case, a piece 

 \J of solid matter of a few millimetres or a few 

 centimetres greatest diameter, placed in space at the earth's 

 distance from the sun, say 150 million kilometres ; for par- 

 ticular example, let us suppose two globes of metal, or rock, 

 or glass, or the bulbs of two thermometers, of a centimetre 

 diameter, one of them coated with black cloth and the other 

 with white cloth, side by side, at a distance of a few centi- 

 metres or metres asunder. For the most extreme simplifica- 

 tion, suppose no other matter in the universe than ether, the 

 sun, and our test globes. From our knowledge of the pro- 

 perties of matter, it is obvious that each of our test globes 

 will, in a few minutes of time, come to a steady temperature. 

 In these circumstances, each globe sends out by radiation as 

 much energy of waves travelling out through ether, as it 

 takes in from the sun ; after it has been long enough exposed 

 to come to a steady temperature. 



§ 2. The internal mechanism in each globe consists of 

 atoms of ponderable matter, with ether permeating through 

 the whole volume of the globe, and locally condensed and 

 rarified in the space around the centre of each atom ; as I 



* Communicated by the Author, having been despatched for Section A 

 of the British Association at Capetown. 



Phil. Mag. S. 6. Yol. 10. No. 57. Sept. 1905. X 



