8 Battery Place, Rothesay
Dec[ember]. 19th 1885.
Dear Mr. Wallace,
I am delighted to find that you are so well pleased with my theory of the origin of the sun's heat. It is very encouraging.
Your considerations strengthen my arguments that the gravitation theory cannot account for the sun's heat. Assuming it as correct that gravity could only have supplied the present rate of radiation for 20 million years, then the time from H-c, when life became possible, to H-h the present time, must be far less than 20 million years; for the rate of radiation at H-c was greater than at present. Geology, however, proves that the time in question must have been more than [2] twice 20 million years.
Your difficulty seems to arise, I think, from your not taking into account the fact that the length of time between H-c and H-h will depend upon the nature of the cooling process. Were the sun solid or possessed a solid crust like that by the earth, its rate of cooling would depend mainly on the conductive power of this crust for heat. Were the crust a bad conductor, the surface would rapidly cool down, and the store of internal heat would last for countless ages. Were it on the other hand a good conductor, like copper, the surface would remain long hot and the store, of course, sooner exhausted. The sun, however, is not solid, but a gaseous mass and cools by an entirely different process. Owing [3] to its gaseous condition, and the way in which it cools (with the consideration by which I need not here enter) the temperature by the surface decreases with excessive slowness.
The great length of the interval between H-c and H-h is mainly due to three circumstances (1) the great mass of the sun (2) the fact that this mass is in a gaseous condition and (3) the enormous store of heat that this mass possesses.
The store of heat is therefore an important factor.
I have left perhaps once and for all I trust, and hope I may be able to [1 word illeg.] a little at my old favourite subject, though terribly crippled by pain in the head.
Yours sincerely | James Croll[signature]
[4]1
Status: Draft transcription [Letter (WCP2181.2071)]
For more information about the transcriptions and metadata, see https://wallaceletters.myspecies.info/content/epsilon
[1] [p. 442]
8 BATTERY PL., ROTHESAY,1
19th December 1885.
DEAR MR. WALLACE, — I am delighted to find that you are so well pleased with my theory of the origin of the sun's heat. It is very encouraging. Your considerations strengthen my arguments that the gravitation theory cannot account for the sun's heat. Assuming it as correct that gravity could only have supplied the present rate of radiation for 20 million years, then the time from H-c, when life became possible, to H-N, the present time, must be far less than 20 million years, for the rate of radiation at H-c was greater than at present. Geology, however, proves that the time in question must have been more than twice 20 million years.
Your difficulty seems to arise, I think, from your not taking into account the fact that the length of time between H-c and H-N will depend upon the nature of the cooling process. Were the sun solid, or possessed of a solid crust like that of the earth, its rate of cooling would depend mainly on the conductive power of this crust for heat. Were the crust a bad conductor, the surface would rapidly cool down, and the store of internal heat would last for countless ages. Were it, on the other hand, a good conductor, like copper, the surface would remain long hot, and the store would, of course, be sooner exhausted. The sun, however, is not solid, but a gaseous mass, and cools by an entirely different process. Owing to its gaseous condition, and the way [2] [p. 443] in which it cools, into the consideration of which I need not here enter, the temperature of the surface decreases with excessive slowness.
The great length of the interval between H-c and H-N is mainly due to three circumstances — (1) the great mass of the sun; (2) the fact that this mass is in a gaseous condition; and (3) the enormous store of heat that this mass possesses.
The store of heat is therefore an important factor. I have left physics once and for all, I trust, and hope I may be able to do a little at my old favourite subject, though terribly crippled by pain in the head. —Yours sincerely, | JAMES CROLL.
Status: Draft transcription [Published letter (WCP2181.6825)]
For more information about the transcriptions and metadata, see https://wallaceletters.myspecies.info/content/epsilon
Please cite as “WCP2181,” in Beccaloni, G. W. (ed.), Ɛpsilon: The Alfred Russel Wallace Collection accessed on 29 April 2024, https://epsilon.ac.uk/view/wallace/letters/WCP2181