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 particles or atoms, and by no one was the atomic theory more firmly maintained than by the contemporary of the later years of Harvey— Isaac Newton. "To me," said he, "it seems probable that God in the beginning formed matter in solid, massy, hard impenetrable particles of such sizes and figures, and with such other properties and in such proportion as most conduced to the end for which He formed them." By Robert Boyle also, to whom Natural Philosophy in the seventeenth century owed much, the theory was held, though he found the explanation of chemical changes in the differences of atomic structure and arrangement of one single form of matter rather than of different elements—a crude foreshadowing of the present day conception by Sir William Crookes of the fundamental matter or "protyle." As is well known, however, it was not until the early years of the last century that the atomic theory received its practical development by John Dalton, since when it has remained at the foundation of physical and chemical science. "Despite attacks and criticisms," says Prof. Clarke in his recent Wilde Lecture, "Dalton's generalisation still holds the field; and from it, as from a parent