C.S. Lewis read Arthur Eddington's "The Nature of the Physical World" and was influenced by it in some particulars. Eddington was a Professor of Astronomy at Cambridge. His book is an exposition, in layman's terms, of the findings of modern (1928) science. I recently read it. (I may be the only man alive who has read "The Nature of the Physical World".) Anyhow, I found two items of interest to Space Trilogy fans.
On page 171, Eddington claims there is a relationship between the Earth's Moon and the fact that Earth has dry-land continents. He goes on to say, "But Venus has no moon, and since it seems so similar to Earth in other respects, it may perhaps be inferred that it is a world which is all ocean - where fishes are supreme."
On page 175, writing of life on Mars, he says, "Finally we may stress one point. Mars has every appearance of being a planet long past its prime; and it is in any case improbable that two planets differing so much as Mars and the Earth would be in the zenith of biological development contemporaneously." Remember the Oyarsa in "Out of the Silent Planet" asking Weston, "But are your wise men so ignorant as not to know that Malacandra is older than your world and nearer its death?"
Just thought some people might be interested. There are some other Lewis-Eddington connections that might be appropriate for other forums.