Why was the Industrial Revolution British? In a recent article published in this Journal, Robert Allen argues that only in England was the price of labor relative to capital high enough to justify the adoption of the labor-saving technologies which characterized the Industrial Revolution.1 To support his argument, he uses the spinning jenny as a case study. The jenny was indeed an important labor-saving technology that was invented and widely adopted in England but not in France. Allen explains this fact by calculating the returns to adopting the jenny in each country: according to his calculations the jenny was profitable in England but not in France.

The present note shows that Allen's conclusions rest on implausible profitability computations. In particular, Allen assumes that output remains constant after the adoption of the jenny while hours worked decrease dramatically. From a theoretical perspective, this is equivalent to an assumption that hours worked move inversely with the marginal product of labor. As soon as these restrictive assumptions are abandoned, the jenny turns out being profitable both in England and in France. Hence the mystery of the adoption of the jenny during the Industrial Revolution remains.