‘In time no less than in regions there are wastes and deserts.’ So I wrote Francis Bacon with medieval science in mind. And when Whewell two hundred years later spoke of‘the almost complete blank which the history of physical science offers, from the decline of the Roman Empire, for a thousand years’, he was only summing up a view of the Middle Ages generally accepted from the seventeenth century down to our own times.

Historians of science did not need much encouragement before passing rapidly and gratefully over the medieval period. Many of the works had never been printed and existed in manuscript only; and everywhere one was confronted with an unfamiliar terminology and barbarous style. That we now know as much as we do about medieval science is due in the first place to the French physicist Pierre Duhem. He re-examined works that had been untouched for centuries and in his monumental treatises of fifty years ago made some disconcerting claims for medieval physicists, especially for his fellow-countrymen of the fourteenth century. To take just one example, Nicolas Oresme emerged as the inventor of co-ordinate geometry, and even as a precursor of Copernicus, although he discussed the motion of the earth only to reject it. Not surprisingly, many took the view that Duhem had overstated his case, but now the medievals had their champion. Issues had been raised, and evidence must be heard.

Unfortunately, the evidence was not forthcoming, unless one accepted Duhem’s quotations at their face value, and overlooked his tendency to tear them out of context and to offer only his translation even when this meant imposing his own interpretation. And there, by and large, the matter rested for thirty years.