By an ancient and honourable tradition, which began last year when I spared you this exercise, the President gives a Presidential Address only once during his term of office, on retirement. A presidential address in the summer season is a privileged occasion. Coming at the end of an active day, it is not the moment for a massive account of research. Rather it is an occasion when one may indulge with privilege in some directed impressionism, and that is what I propose to do.

In France, as in other European countries, especially Britain and Germany, the nineteenth century was a period of great progress and achievement in science. This would still have been true if Claude Bernard and Louis Pasteur had been the only outstanding French scientists of the nineteenth century, whereas there were, of course, many others apart from an impressive number of brilliant French mathematicians. Nevertheless, although it was a great century for French science there was perhaps something rather disappointing about it, and something rather ingrowing about the attitude of French scientists towards scientific developments in other countries. For example, the French took it hard that the creator of the theory of evolution should have been an Englishman, remembering too late Darwin's predecessor Lamarck, and they certainly were very slow in accepting Darwin's theory of evolution.1 Again, the French may have felt that after the important contributions of French scientists such as Coulomb, Poisson, Biot and, above all, Ampère, the theory of electricity and magnetism which is today principally associated with the names of Faraday and Maxwell should have been created by a Frenchman. Once again this new theory was only accepted very slowly and hesitantly, and even unwillingly, in France—one thinks, for example, of the criticisms levelled at the theory by Pierre Duhem in his “The Aim and Structure of Physical Theory”.2 Of course it might be that if one knew how to weigh properly the various achievements of French scientists in different branches of science one would find that, allowing for her rather static population during the nineteenth century, the total contribution of France compared well with those of Britain and Germany. Nevertheless, in one case at least, that of theoretical physics, there seems to have been an unmistakable failure to live up to the promise of the beginning of the century. The purpose of this paper is to advance possible reasons to explain this failure.

This paper summarizes ideas about the nature of gases proposed during the period following the discovery of Boyle's law. Particular stress is laid on the hypotheses of the Bernoullis, and later, on the equally speculative work of Herapath. Reasons for the success of Herapath's theory, and the neglect of Daniel Bernoulli's are discussed, but it has not been thought necessary to take the story beyond the initial acceptance of Herapath's theory by J. P. Joule, because the paper is concerned only with the antecedents of the modern kinetic theory.

The “Scientific Revolution” of the seventeenth century cannot adequately be assessed without an appreciation of the achievements and limitations of those, whether giants or dwarfs, on whose shoulders Galileo and his contemporaries stood. And since for many historians Galileo's main contribution lies in the mathematization of the natural world and especially of time and motion, particular interest attaches to medieval treatises dealing with these questions, above all to those which were in widespread demand early in the sixteenth century.