WCP2899

[1]^{1, 2}

Minsmere

Dunwich Saxmundham

Suffolk

Jan[uar]y 20th 1908

Dear Sir,

There is a print in your book in "Man's Place in the Universe" which I have tried in vain to verify: and as it is essential (in part at least) to the argument, I should be much obliged if you could explain the difficulty. You were good enough to write to me about some other points in the book, in reply to a letter of mine in 1905.

On p 266 it is stated that "the [2] smaller planets Mercury & Mars, have not sufficient mass to retain water-vapour" and on p 267 "as it is almost certain that it contains no water, its polar snows being caused by carbonic acid or some other heavy gas."

The velocity from infinity to the Earth, or Mars is easily calculated from their accepted masses. I worked them all out from the formula =- where =- [,]

=C+ or = given when r=[,] v=0[.]

[3]³ No values for the Earth & for Mars come net the same as those calculated in Lowell's "Mars"[.]

When in Birmingham last June I called on D^r Soyatiy[?] and he looked at for me the molecular velocities of Hydrogen water-vapour &c. and showed me that the mole average molecular velocity of water vapour is well within the velocity from infinity for Mars; indeed there seemed no reason for question about the presence of water-vapour in Mars, on the score of the Kinetic theory of gases. If this be [4] so, it is not easy to see why "the mass of Mars is not sufficient to retain water-vapour."

I see that Mr. Lowell in his most recent book points out that frozen CO₂ passes per saltum from the solid to the gaseous form, with no appreciable liquid interval between: while the polar caps of Mars are always surrounded, as they melt, by a blue band; presumably water at certain sessions they are [1 word illeg.] or hooded with a semi-transparent mist. Neither of these seems to fit in with the [5]⁴ hypothesis that the polar caps are congealed CO₂.

Is Lowell accurate about his chemistry or would frozen CO₂ show a belt of liquid CO₂ all round it, when melting in the sun?

If Mars has an atmosphere & enough water to produce its huge polar caps, obviously organic life would be possible there: and the seasonal changes in the large dark patches do not appear to be explicable by any hypothesis of optical illusion. Barnard^{2 of the Lick Observatory} hold the [6] geometrical patterned "canals" to be an optical illusion: but the large patches are as plainly observable with good telescopes, as the smaller craters of the Moon. Vegetation, following in its growth in the melting of the polar snows, seems to be the only possible explanation. And if vegetable life has evolved on Mars, by all principles of biology surely animal life must have evolved pari passu. And since Mars is obviously in its old age & has pretty well gone through its biological cycle, it would be [7]⁶ contrary to the analogy[?] of evolution to assume that some high type of rational animal has not been evolved there.

Given this — then Lowell's theory of the Canals is not inherently improbable. Which probably at present is all that can safely be said on the subject.

But what puzzles me is that you set aside, à priori, all possibility of organic life in Mars for a reason which seems to me to be contrary to the [8] accepted facts about the Kinetic theory of gases & the measured masses of the planets.

I should be much obliged if you could explain this apparent paradox.

Very truly yours | James A Aldis³[signature]

Dr Alfred R Wallace.