192 Dr. M. Smoluchowski de Smolan on 



necessary to reheat it to a higher temperature than the final 

 temperature of the preceding heating*. 



I have elsewhere attempted to interpret the foregoing 

 series of experiments, but I do not feel justified in troubling 

 your readers with opinions that may be of little interest to 

 them. 



Finally, 1 will take this opportunity of tendering my 

 gratitude to Prof. K. Angstrom, on whose initiative I began 

 my researches. 



Upsala, 1896. 



XIV. On Conduction of Heat by Rarefied Gases. 

 By M. Smoluchowski de Smolan, Ph.D.-f 



1. AT the same time when this year's first number of 

 J\. the Philosophical Magazine appeared, containing 

 Mr. 0. F. Brush's very interesting paper " On Transmission 

 of Radiant J Heat by Gases at Varying Pressures," I published 

 in Wiedemann's Annalen (vol. lxiv. p. 101, 1898) the results 

 of an experimental investigation of mine on quite a similar 

 subject, and conducted in quite a similar way, though quite 

 independently, of course, of Mr. Brush's. 



The design of my work was somewhat different, however. 

 His research, which is of a purely experimental character, 

 extends over the general laws of cooling of bodies in gases at 

 various pressures, including the effects of convection-currents, 

 of radiation, and conduction of heat. I tried, on the contrary, 

 to eliminate the first two effects, considering former researches 

 of Kundt and Warburg, and confined my attention to the con- 

 duction of heat, and especially to the modifications of it 

 arising at very low gas-pressures, in respect of which the 

 kinetic theory of gases gives some remarkable suggestions 

 which had not been examined before. 



In order to explain these, I may be allowed to remind the 

 reader of certain points in the mathematical theory of con- 

 duction of heat. 



2. As is known, Fourier based his theory upon the 

 assumption that the quantity of heat flowing through a 

 body in a given direction is proportional to the corresponding 



* This is, of course, only shown for the conditions of heating in 

 question, and it is not thereby proved that the heating extended over a 

 longer period at the final temperature of the preceding heating is without 

 effect upon the contraction of the rod. 



f Communicated by the Author. 



% Would it not have been preferable to omit the word "radiant"? 

 It can be used only in connexion with the ' 'aether-line " in Mr. Brush's 

 observations, not with convection or conduction of heat. 



