1. Historical studies

It is my belief that in-depth studies of concrete episodes can often teach us much more than general and abstract cogitation can; the idea is not to abandon abstract questions, but to see them played out in action. In addition, I believe that the nature of scientific thinking can be exhibited more clearly when we consider simple and elementary items of knowledge, rather than the current cutting-edge episodes that are encased in formidable technical details.

I am engaged in a historical-philosophical study of the investigative processes that led scientists to the modern conception of the nature of air and water in the decades around 1800. At the start of the historical period under consideration, both of these substances were Aristotelian elements; by the end of the period air was established as an accidental mixture of various gases, and water as a chemical compound of hydrogen and oxygen.

It may seem strange that I should choose such plainly observable substances when attempting to illustrate the nature of evidential reasoning about the unobservable. But much as we can readily splash water on our faces and feel the spring of air captured in a balloon, the microscopic compositions of these substances are entirely unobservable. As an illustration, consider the fact that John Dalton, the originator of chemical atomism, believed that water was not H2O, but HO; frankly admitting that neither molecular formulae nor atomic weights were directly determinable from observations (though knowing one allows us to infer the other), Dalton invoked a "rule of simplicity" that dictated the adoption of simplest possible molecular formulae. It took at least 50 years for chemists to reach a consensus against Dalton on this matter, which was one of the most painful headaches of 19th-century chemistry.

A series of historical studies recommend themselves along the same lines, concerning the following major scientific events and questions: the discovery and characterisation of oxygen; the production and classification of "factitious airs"; the mechanism of the solution of gases in water, and the evaporation of water into air; the theory of rain, cloud-formation, and other meteorological phenomena; debates on the composition of water, based on experiments attempting to show its synthesis and analysis; debates surrounding the reality of atoms, and the determination of atomic weights and molecular formulae.

In each case, I will identify and scrutinise the evidential base and the nature of evidential reasoning that led to the adoption of the answer that has now become an item of scientific common sense.

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