My dear Barrett,--Thanks for your letter, and your friend Prof. Stroud's. I have come to the sad conclusion that it is hopeless to get any mathematician to trouble himself to track out Lowell's obscurities and fallacies.... So, being driven on to my own resources, I have worked out a mode of estimating (within limits) the temperature of Mars, without any mathematical formulae--and only a little arithmetic. I want to know if there is any fallacy in it, and therefore take the liberty of sending it to you, as you are taking your holiday, just to read it over and tell me if you see any flaw in it. I also send my short summary of Lowell's _Philosophical Magazine_ paper, so that you can see if my criticism at the end is fair, and whether his words really mean what to me they seem to....--Yours very sincerely, ALFRED R. WALLACE. * * * * * TO MR. F. BIRCH _Sept. 12, 1907._ Dear Fred,-- ... For the last two or three months I have had a hard struggle with Mars--not the god of war, but the planet--writing a small book, chiefly criticising Lowell's last book, called "Mars and its Canals," published less than a year back by Macmillan, who will also publish my reply. _I_ think it is crushing, but it has cost me a deal of trouble, as Lowell has also printed a long and complex mathematical article trying to prove that though Mars receives less than half the sun-heat we do, yet it is very nearly as warm and quite habitable! But his figures and arguments are alike so shaky and involved that I cannot get any of my mathematical friends to tackle it or point out his errors. However, I think I have done it myself by the rules of common sense....--Your sincere friend, ALFRED R. WALLACE. * * * * * TO MR. H. JAMYN BROOKE _Old Orchard, Broadstone, Wimborne. December 2, 1910._ Dear Sir,--Your "monistic" system is to me a system of mere contradictory words. You begin with three things--then you say they are correlated with one substance--coextensive with the universe. This you cannot possibly know, and it is about as intelligible and as likely to be true as the Athanasian Creed!--Yours truly, ALFRED R. WALLACE. * * * * * TO PROP. KNIGHT _Old Orchard, Broadstone, Dorset. October 1, 1913._ Dear Mr. Knight,--I have written hardly anything on the direct proofs of "immortality" except in my book on "Miracles and Modern Spiritualism," and also in "My Life," Vol. II. But my two works, "Man's Place in the Universe" (now published at 1s.), and my later volume, "The World of Life," form together a very elaborate, and I think conclusive, scientific argument in favour of the view that the whole material universe exists and is designed for the production of immortal spirits, in the greatest possible diversity of nature, and character, corresponding with ... the almost infinite diversity of that universe, in all its parts and in every detail....--Yours very truly,