WCP6896

[1]

Waldron Edge, Duppas Hill, Croydon

April 1st, 1879

Dear Sir

As you were so kind as to give me some mathematical information before, I venture to trouble you again.

I am going over the whole question of the glacial epoch & warm periods in the arctic regions for a book I have in hand, and after considering the question in all its bearings I am led to the conclusion that changes of excentricity alone (combined with precession &c.) will not explain the facts,— but that they require a great diminution of the excentricity obliquity of the ecliptic. I wish to ask you whether the considerations mentioned by Ball in his paper on the "Climate of the Glacial Period" — (irregularity of the equatorial protuberances, inequality of land & water in two hemispheres, ice-accumulation at poles &c.) may possibly have had an effect in causing an increase in the obliquity, or [2] whether the alternate accumulations of ice at poles, each for 10,500 years, with alteration of centre of gravity, could affect it.

Would the increase of mass of sun by falling in of meteors (which may be very considerable) cause any increase of the obliquity?

I seems to me that if we could have a permanent decrease of the obliquity in geologic times, we should have, in combination with the phases of excentricity, & changes of land and sea, a complete explanation of the geological phenomena of climate, which, without that, is a hopeless puzzle.

As yet all the ^numerous arctic deposits, from the Miocene backwards indicate warm or mild climates, none arctic conditions. This is not explicable on theory of excentricity with present obliquity for these warm climates should be the exception, not the <rule.> [3]

Astronomers have generally been so positive about the narrow limits of variation of obliquity that they have frightened geologists away from it. I think you have written on the subject, and so are no doubt able to speak as to the possibilities.

Yours very faithfully | Alfred R. Wallace [signature]

Revd. O. Fisher

P.S. Four months continued radiation uncompensated by a gleam of sun-heat must produce an intense cold incompatible with luxuriant vegetation even though the rest of the earth were exceptionally warm.