Two major problems in understanding Joseph Priestley (1733–1804) are that he wrote so much and over such a wide area. The nineteenth-century edition of his collected works fills 25 volumes—and that leaves out the science! In discussing a man like Priestley, therefore, one cannot hope in a single lecture to do justice to the wide range of his interests or even to summarise adequately his many contributions to science. Fortunately much of the scientific work is fairly well known, for example his discovery of many new gases or ‘airs’, as he preferred to call them. It might be appropriate, therefore, to try to put Priestley's pneumatic chemistry in a wider context and in particular to relate it to his career. Priestley was not only an important man of science. He was also an outspoken theologian, a literary figure and a family man, and all of these roles (and several others, including his political role on behalf of Dissenters) will have to be taken into consideration when the definitive biography is written.

Siméon Denis Poisson (1781–1840) was a major figure in French science throughout the first forty years of the nineteenth century. Though his papers lack the brilliant mathematical creativity of some of those published by even more gifted contemporaries such as Joseph Fourier (1768–1830) and Augustin-Louis Cauchy (1789–1857), they nevertheless display a formidable talent for mathematical analysis, applied with great industry and success in a large number of investigations ranging over the whole domain of mathematical physics. Several were of such importance that even on their own they would have sufficed to win him lasting fame.

The change in the physiological conception of body fluid during the Seventeenth Century exemplifies the beginning of changes in chemical ideas away from humours as irreducible components of fluid systems towards water as the common solvent of an indefinitely large range of solutions. Against the Galenic humoral view of body fluids J.-B. van Helmont (1579–1644) postulated ‘latex’, a humour distributed through the body and common to several body fluids. The theory of latex explained experimental findings and provided a basis for Helmont's introduction of diuretics into the treatment of dropsy. Francis Glisson (1597–1677) adopted the theory of latex. In this paper it is shown that Helmont contradicted, in part at least, the distinctness of humours by a doctrine of a common reservoir from which various body fluids are drawn. It is further argued that, on the available evidence, Helmont is the originator of this idea of a common reservoir. Through hitherto unremarked and unpublished manuscript evidence, it is shown that Glisson, in adopting the theory of latex, and its therapeutic application, modifies and extends it. In the manuscripts Glisson expresses himself in the language of Helmontian philosophy. Given Glisson's known influence (in, for example, spreading Harvey's doctrine of the circulation), the question arises what part, if any, is attributable to him in the transmission of the doctrine of the common reservoir. From the point of view of experimental science, that doctrine makes a break with the past no less radical than does, say, that of the circulation. It appears that we have here yet another major contribution of Helmont to the scientific revolution with, through Glisson, a possible channel of transmission of this contribution.