In 1906 there appeared in The Philosophical Transactions of the Royal Society, Whitehead's memoir "On Mathematical Concepts of the Material World"¹ (MC). Its object was to show how one could construct alternative models of the physical world. Although Whitehead had worked in pure mathematics and logic, his Fellowship dissertation at Trinity,² as we have seen, had been on Clerk Maxwell's theory of electromagnetism, in which he seems to have retained an interest throughout his life. In this memoir he brings together axiomatic theory and the physical view of nature in terms of the continuity assumed in electromagnetic theory. These two strands of thought are to be found running through his later writings, namely, an interest in abstract structure and its relation to the physical world.