Many mathematicians know their details but are ignorant of the philosophical characterisation of their science.’ It was A. N. Whitehead who wrote this. He himself made an admirable effort to supply the defect. Assuming that no recognised philosopher knew enough of the details of mathematical science to give a reliable account of it, he read, besides Plato and Aristotle, a selection of seventeenth-century writers—particularly Descartes, Newton, Locke, Hume, Kant—who either knew enough about mathematics to be helpful, or little enough to show in what new way philosophy must be handled to meet the mathematicians’ need. He then wrote Process and Reality. An Essay in Cosmology, which he delivered as the Gifford Lectures for 1927-28 and published in book form in 1929. It is less exclusively addressed to mathematicians than the earlier work he had begun with Bertrand Russell and then abandoned; but its whole drive aims at setting the sciences that use mathematics in their full philosophical and spiritual context. By the time it was finished the revolution worked in physics by the theories of quanta and relativity was firmly established. The work took into account, with full approval, the new cosmological outlook the change implied.