This book, published in 1972, takes a look back at "the books that everyone read" between 1900 and 1939, and what we can understand about why these books were read and who read them. Some of the titles here are still well-known and a few are still in print (Precious Bane, The Constant Nymph and The Riddle of the Sands are all included); others are remembered but probably very little read now (The Blue Lagoon); while some are simply obscure (have you heard of The Beloved Vagabond? neither had I). Cockburn's book is, among other things, a very useful guide to these books, including details of plot and extensive quotations, which give you a good sense of the writer's style.
Cockburn's argument is that books are popular because they fulfil a need for the expression of ideas that is not available elsewhere to the reader; because writers understand this, and because they have an affinity with the reader that allows them to write such books; and because of the craft of the writer concerned. While he acknowledges that the 'rattling good yarn' is often an avowed reason for a book's popularity, Cockburn has no truck with the idea that the realist or genre writers of the early twentieth century eschewed style, pointing out how carefully you need to construct books of this sort in order to make them readable. He also argues strongly for bestsellers being read by a middle-class audience. If you've read much early twentieth century fiction, you'll probably have come across descriptions of novels as being fit only for housemaids. There were a lot of housemaids before 1939, but not enough to push a novel like E.M. Hull's The Sheik quite so far up the bestseller lists. Cockburn suggests that - whatever they said in public about their reading habits - middle-class readers read books like The Sheik, and they did so because they enjoyed them.
Some of these books established a genre. Erskine Childers' The Riddle of the Sands is a prototype spy novel (for an enthusiastic and enthusing review of this book, try Kate Macdonald's podcast at reallylikethisbook.com, in fact try all her podcasts as they are an excellent way to spend ten minutes). The Sheik, a potent blend of exoticism and violent sex, not only inspired middle-class women to tour Morocco looking for a Sheik of their own, but has a current great-grandchild in the shape of Fifty Shades of Grey. Cockburn's political position (he was a well-known proponent of communism) is overt in this text, and he castigates readers for claiming that they have no affinity with books that promote racism or misogyny which they choose to read for pleasure: "There were other books on the library shelf". Cockburn was a journalist and the style of this book bears that out; his writing is incisive and amusing. This sometimes sits oddly with the indigestible prose he quotes from the bestsellers under consideration.
This book is out of print, although there are a few very cheap secondhand copies around and it seems to be fairly easy to find in libraries.