See — Temperature of the Sun and Ages of Stars and Nebulae. 23 



already, " though of course not in the shape of a formula in- 

 troducing the idea and symbol of absolute temperature," it 

 seems proper to offer, at this time, a connected view of the 

 whole question. How far the author had been anticipated in 

 the discovery of this law, and how he became acquainted with 

 Hitter's work after writing the article in A. N. 3585, has been 

 sufficiently set forth in the Astronomical Journal , No. 455. 

 But it should be added here that at the time of composing 

 that article, the writer was not aware of the existence of Hit- 

 ter's earlier paper in Wiedemann' 's Annalen for 1878, s. 543,* 

 in which he reached a formula and a number of conclusions 

 essentially identical with those recently published. The scien- 

 tific public will be able to judge how far these results of Hit- 

 ter were known among astro-physicists, and what influence, 

 if any, they had already exercised upon astronomical thought. 

 In the present paper, written since May 1, 1899, it is to be 

 understood that the author has availed himself freely of the 

 works of Hitter f as well as of those of Lane % and Lord 

 Kelvin, fl 



3. On the convective equilibrium of a gaseous mass. 



Gaseous stars are continually losing heat by radiation, 

 and contracting in consequence of the loss of heat, thereby 

 growing- denser and hotter. In stars of mature age the 

 radiation is chiefly from the surface layers, and as these ex- 

 posed portions soon cool off, it is evident that the continuity 

 of the energy supply is maintained by the circulation of the 

 mass in a state of convective equilibrium. Accordingly, we 

 must explain the nature of the circulation and adiabatic con- 

 traction which sustains the steady light and heat of the stars. 



A mass of gas changes adiabatically when it neither gains nor 

 loses heat from contact with its surroundings, but expands 

 and contracts in such a way as to adjust itself to the condi- 

 tions which envelop it. 



* Professor Nipber first called attention to this paper, in one of the im- 

 portant contributions which he recently submitted to the Academy on this 

 subject, Transactions, Vol. IX, No. i. 



t Wiedemann's Annalen, 1878 to 1882. 



X American Journal of Science, July, 1870. 



1 Philosophical Magazine, 1887, p. 287. 



