688 Lord Kelvin : The Problem of 
and they express, I believe, the views he held while writing the 
earlier sections. 
The statement of mathematical solutions and numerical results 
separately, as an Appendix to the paper, under my own name, is 
in accordance with Lord Kelvin's wishes. 
George Green, 
Secretary. 
§ 1.* TF a fluid globe were given with any arbitrary dis- 
JL tribution of temperature, subject only to the 
condition that it is uniform throughout every spherical 
surface concentric with the boundary, the cooling, by radia- 
tion into space, and consequent augmentation of density of 
the fluid at its boundary, would immediately give rise to an 
instability according to which some parts of the outermost 
portions of the globe would sink, and upward currents would 
consequently be developed in other portions. In any real 
fluid, whether gaseous or liquid, this kind of automatic 
stirring would tend to go on until a condition of approximate 
equilibrium is reached, in which any portion of the fluid 
descending or ascending would, by the thermodynamic action 
involved in change of pressure, always take the temperature 
corresponding to its level, that is to say, its distance from 
the centre of the globe. The condition thus reached, when 
heat is continually being radiated away from the spherical 
boundary, is not perfect equilibrium. It is only an approxi- 
mation to equilibrium, in which the temperature and density 
are each approximately uniform at any one distance from 
the centre, and vary slowly with time, the variable irregular 
convective currents being insufficient to cause any consider- 
able deviation of the surfaces of equal density and temperature 
from sphericity. 
§ 2. The problem of the convective equilibrium of tempe- 
rature, pressure, and density, in a wholly gaseous, spherical 
fluid mass, kept together by mutual gravitation of its parts, 
was first dealt with by the late Mr. Homer Lane, who, as we 
are told by Mr. T. J. J. See, was for many years connected 
with the U.S. Coast and Geodetic Survey at Washington. 
His work was published in the American Journal of Science, 
July 1870, under the title " On the Theoretical Temperature 
of the Sun " f. 
* § 1 is extracted from " On Homer Lane's Problem of a Spherical 
Gaseous Nebula," Nature, Feb. 14, 1907. 
f The real subject of this paper is that stated in the text above. The 
application of the theory of gaseous convective equilibrium to sun heat 
and light is very largely vitiated by the greatness of the sun's mean 
density (1*4 times the standard density of water). Common air, oxygen, 
and carbonic acid gas show resistance to compression considerably in 
