There were two giants in popular science writing in the late 1920s, certainly in the sub-sector of popular writing about physics and astronomy: A. S. Eddington and James Jeans, both physicists working at Cambridge University.  Works by both sold astonishingly well, but if the qualities of the writing are considered, Eddington should have outsold Jeans, and he didn’t.

My interest in how science became available to literary authors led me early on to popular science writing.  One might argue that popularity is a quality of the style of writing (its mode of address, the way it introduces and deploys technical terms, and the way it frames strictly scientific questions with humanistic concerns), and that popularity in terms of sales figures is a separate issue, but, for better or for worse, my initial impulse was to pursue sales figures.  Eddington, Cambridge professor and author of The Nature of the Physical World (1928), was a faintly obsessive record keeper, especially when it came to numbers, and the notebooks held by Trinity College, Cambridge, record the lengths of his cycle rides, the weights of his prize medals, and — most usefully to me — the annual sales figures for each of his books.  For other 1920s and 1930s authors like James Jeans, it is possible to find out about print runs from the archives of Cambridge University Press. Here’s one of the less exciting pages of my D.Phil., concerning Eddington’s Space, Time, and Gravitation (1920):

The upturn in sales in 1942 is something I’ve seen in Herbert Read’s figures too, and I think it’s more widely recognised; people were staying at home more because of the war-time blackout regulations. The upturn in sales in 1929 was probably caused by the success of The Nature of the Physical World, published in November 1928; although Space, Time, and Gravitation, is a more technical work, it’s likely that the later work stimulated interest and demand.

Jeans’s career as a popular science writer had begun with Eos, or the Wider Aspects of Cosmogony (1928), in Kegan Paul’s To-Day and To-Morrow series, and had continued with The Universe Around Us (1929). But his biggest success was The Mysterious Universe (1930), an expanded version of the Rede Lecture which he delivered in November 1930.  Published the day after the Rede Lecture, by the end of December it had sold 70,000 copies in the UK.  The Nature of the Physical World had managed about 2500 in its first two months.  Jeans’s book, shorter than Eddington’s, is a lucid exposition of developments in modern physics, but Jeans didn’t have Eddington’s gift for taking difficult physical concepts, at times counter-intuitive ones, and rendering them tangible.  Nor does Jeans deliver coups-de-theatre such as Eddington’s opening scene in which he stands before two tables, the one his everyday table, the other a table as described by science.  If I were selecting one to be reprinted as a classic of its time, it would be Eddington’s; but whether because of price or brevity or some freak whim of the marketplace, it was Jeans’s work that found more prominence.