For Hicks, then, thinking back his argument to a "more cumbrous but more realistic form" involved making an unexplained leap from the observation in Chapter V, consistent with Chapman's theory and historical evidence, that "[p]robably it had never entered the heads of most employers that it was at all conceivable that hours could be shortened and output maintained" (p. 107) to the claim in Chapter XI that, "[a] very moderate degree of rationality on the part of employers will thus lead them to reduce hours to the output optimum as soon as Trade Unionism has to be reckoned with at all seriously" (p. 218). It is not a question of whether Hicks's assertion was right or wrong. His claim simply didn't follow from his own premises and, in key respects, contradicted them.
Although Hicks's non sequitur feat of "realism" may be one element in the disappearance of Chapman's theory, surely it can't be held solely responsible for its eclipse. For an explanation of that, we need to turn to a subsequent general shift in formal economic analysis (in which Hicks was deeply involved) that took place in the 1930s. This shift inherited some of its fundamental premises from the thought of Leon Walras, Vilfredo Pareto and Enrico Barone, proponents of the Lausanne school of economics.
Abstract: Sidney Chapman's theory of the hours of labour, published in 1909 in The Economic Journal, was acknowledged as authoritative by the leading economists of the day. It provided important insights into the prospects for market rationality with respect to work time arrangements and hinted at a profound immanent critique of economists' excessive concern with external wealth. Chapman's theory was consigned to obscurity by mathematical analyses that reverted heedlessly to outdated and naïve assumptions about the connection between hours and output. The Sandwichman is serializing "Missing: the strange disappearance of S. J. Chapman's theory of the hours of labour" on EconoSpeak in celebration of the centenary of publication of Chapman's theory. (To download the entire article in a pdf file, click on the article title.)