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from without we know that it comes from within. As Mr Benn puts it, we have extended the atomistic method from "matter" to motion. Harvey's con- temporary, Francis Bacon, sagaciously guessed that heat is an expansive motion of particles; but he regarded heat and cold as two contrary principles. Almost in the same generation the brilliant John Mayow perceived a substance in the air "allied to saltpetre," which passed in and out of the blood by the way of the lungs or placenta. "Innate heat" then gave way to phlogiston; but it was not till the discovery of oxygen and of the conservation of energy that we attained a theory of energy, and finally got rid of "matter and form," and of all the thicket of metaphysics, relating thereto; through which in the day of Ilarvey no mind, however mighty, could have made its way.
In the history of medieval thought we must always bear in mind that in neither of its two periods were theology, logic, metaphysics, psychology, or even physics, fully differentiated; and before the Arabian literature they were not differentiated at all'. Logic, which for us is but a drill, and, like all
1 The word "philosophy" in the Middle Ages signified the pursuit of knowledge of things human and divine, and of the causes of them. It was often divided into Physics, Ethics and
