Pitcullen Crescent
Perth
Sept[ember]. 9th 1889
My Dear Sir,
Referring to your letter of 25 Ult.[?] I think your difficulty arrises from overlooking the fact that, according to the impact theory, condensation can only take place as the nebula looses its heat; whereas according to the gravitation theory condensation is required to produce the heat. Take the case of the solar nebula. According to the latter theory, when the materials had condensed so as to occupy only the space, say, included within the earth's [2] orbit there would be comparatively little heat generated, and the store of energy possessed by this nebula, which we shall now call the sun, would be small indeed. I have not computed the amount, but I am certain that it would not be sufficient to supply the present rate of solar radiation for many thousand years. The mass would require to be condensed to a space far less than that included within the orbit of Mercury before a store sufficient to supply the present rate of radiation [3] for at least one or two millions of years. But by in regard to the impact theory, by the time the nebula had cooled and condensed to the earth's orbit it might probably possess some hundreds of millions of year's heat.
I trust that these considerations will make the matter plain.
Have you seen Dr. Huggin's paper on the great nebula in Grion? In case you have not I have sent you by post which you can return at your [4] leisure. It goes a good way to establish the theory. If that nebula had originated by condensation it could not consist of a gas so tenuous, and of such a low density and high temperature.
Yours very truly | James Croll [signature]1
Status: Draft transcription [Letter (WCP2413.2303)]
For more information about the transcriptions and metadata, see https://wallaceletters.myspecies.info/content/epsilon
[1] [p. 468]
5 PITCULLEN CRESCENT, PERTH,
9th September 1889.
Alfred R. Wallace, Esq.
MY DEAR SIR, — Referring to your letter of 25th ult., I think your difficulty arises from overlooking the fact that, according to the Impact theory, condensation can only take place as the nebula loses its heat, whereas, according to the Gravitation theory, condensation is required to produce the heat. Take the case of the solar nebula. According to the latter theory, when the materials had condensed so as to occupy only the space, say, included within the earth's orbit, there would be comparatively little heat generated, and the store of energy possessed by this nebula, which we shall now call the sun, would be small indeed. I have not computed the amount, but I am certain that it would not be sufficient [2] [p. 469] to supply the present rate of solar radiation for many thousand years. The mass would require to be condensed to a space far less than that included within the orbit of Mercury, before a store of heat sufficient to supply the present rate of radiation for at least one or two millions of years. In regard to the Impact theory, by the time the nebula had cooled and condensed to the earth's orbit, it might probably possess some hundreds of millions of years’ heat.
I trust that these considerations will make the matter plain.
Have you seen Dr. Huggins'1 paper on the great nebula in Orion? In case you have not, I have sent you by post a copy which you can return at your leisure. It goes a good way to establish the theory. If that nebula had originated by condensation, it could not consist of a gas so tenuous, and of such a low density and high temperature. —
Yours very truly, | JAMES CROLL.
Status: Draft transcription [Published letter (WCP2413.6826)]
For more information about the transcriptions and metadata, see https://wallaceletters.myspecies.info/content/epsilon
Please cite as “WCP2413,” in Beccaloni, G. W. (ed.), Ɛpsilon: The Alfred Russel Wallace Collection accessed on 2 May 2024, https://epsilon.ac.uk/view/wallace/letters/WCP2413