the same way as a naturalist would study questions of physical science. They began by collecting facts, and when they ventured upon generalisations, they resorted to induction. They sometimes made hypotheses, but they attributed no more importance to these suppositions than Darwin attributed to his hypothesis concerning the origin of new species by means of natural selection in the struggle for existence, or that Mendéléeff attributes to his "periodic law." They looked upon them as suppositions affording a temporary explanation ("working hypotheses") and facilitating the grouping of facts, as well as their subsequent study; but these suppositions were not accepted before they were confirmed by applying them to a multitude of facts, and explained in a theoretical, deductive way; and they were not considered as natural "laws"—that is, proved generalisations—so long as they had not been carefully verified, and until the causes of their constant exactitude had been explained.
When the centre of the philosophic movement was transferred from Scotland and England to France, the French philosophers, with that perception of system which belongs to the French thinkers, began to construct all human sciences, both natural and historical, on a general plan and on the same principles. They attempted to construct "generalised knowledge"—that is, the philosophy of the Universe and its life—upon a strictly scientific basis. They consequently put aside all metaphysical constructions of the preceding philosophers, and explained all phenomena by the action of those same physical forces (that is to say, mechanical actions and reactions) that sufficed them to explain the origin and the evolution of the terrestrial globe.
It is said that when Napoleon I. remarked to Laplace that in his "Exposition of the System of the Universe" the name of God was nowhere to be found, Laplace answered: "I nowhere felt the need of that hypothesis." But Laplace did more. He never resorted either to the grand metaphysical words behind which lies the incomprehension or the obscure semi-comprehension of phenomena, together with the inability to consider facts in their concrete form, as measurable quantities. Laplace dispensed with Metaphysics as well as with the hypothesis of a Creator; and although his "Exposition of the System of the Universe" contains no mathematical calculations and was written in a style comprehensible to all educated readers, mathematicians could later on express each separate thought of that work in mathematical equations—that is to say, as conditions of equality between two
