In the period 1700-1850 a major transition in natural philosophy took place: from Newton"s concept of passive matter activated by ethereal and active principles, to the conception of nature as a self-contained system, its activity being seen in terms of the energy and field principles which were internal to the natural order. Without neglecting the scientific context, Dr Harman"s approach is from the standpoint of the history of ideas. The first part of the volume deals with the British tradition of speculation about the nature of matter, ether and force; the second with the Continent, with the Leivnizian and Kantian critiques of Newtonian natural philosophy, and the development of Helmholtz"s principle of the conservation of energy. The metaphysical and theological dimensions to matter theory are seen as fundamental to this profound shift in sensibilities; they did not determine the scientific practice, but they constrained its form and shaped the structure of scientific thought.