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 it." It is an error to suppose that recent research has removed Dalton's atomic theory or rendered it obsolete. We now know that Dalton's atoms are not atoms, but it is still true that "elements combine in constant proportions by weight." In the words of Sir George Darwin: "The vast edifice of modern chemistry has been built with atomic bricks." From the later work of to-day we know that the atom is not the ultimate form of matter. There are corpuscles and ions inconceivably smaller; but, says Professor A. Smithells, "few will deny that the atomic theory stands to-day an indispensable instrument for productive work; it has neither had its day nor ceased to be. We are now called upon to subdivide our atom, to credit it with an unsuspected store of energy, to consider it a congeries of unsubstantial electrons. There can be no possible objection from our side; it will undo nothing that has been done, and we may have good hopes that it will lead to the doing of many new things in chemistry."

In 1802 Dalton ascertained the composition of the atmosphere, namely, that a hundred volumes contain twenty-one volumes of oxygen and seventy-nine volumes of nitrogen. In 1804 he was asked to give a course of lectures at the Royal Institution of London; and in these lectures he explained his views on the absorption of gases by liquids, on the constitution of gases, etc. As a lecturer, his manner lacked charm and gracefulness, but in spite of these defects his genius was greatly appreciated.