Descartes' two treatises of corpuscular-mechanical natural philosophyLe Monde (1633) and the Principia philosophiae (1644/1647)differ in many respects. Some historians of science have studied their significantly different theories of matter and elements. Others have routinely noted that the Principia cites much evidence regarding magnetism, sunspots, novae and variable stars which is absent from Le Monde. We argue that far from being unrelated or even opposed intellectual practices inside the Principles, Descartes' moves in matter and element theory and his adoption of wide swathes of novel matters of fact, were two sides of the same cointhat coin being his strategies for improving the systematic power, scope and consistency of the natural philosophy presented in the Principia. We find that Descartes' systematising strategy centred upon weaving ranges of novel matters of fact into explanatory and descriptive narratives with cosmic sweep and radical realist Copernican intent. Gambits of this type have recently been labelled as cosmographical' (the natural philosophical relating of heavens and earth in contemporary usage). Realist Copernican natural philosophers, from Copernicus himself, through Bruno, Gilbert and Galileo did this to varying degrees; but, we suggest, Descartes presented in Books III and IV of the Principia the most elaborate and strategically planned version of it, underneath the ostensible textbook style of the work.
