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Rh all significance, so long as the idea was fruitful in the classification of known facts, and prepared the way for new generalizations."

Chemistry had made rapid advances under the phlogistic theory for a century, but the idea was now to be brought to the test of quantitative examination. The introduction of the balance threw a new light upon the subject, and, under its application, the assumptions of the phlogistic system of chemistry proved to be entirely erroneous. The effect of careful weighing was to show that metals and other combustible bodies, in burning, grew heavier; that there was no subtraction or loss of any thing, but always an addition; and that the compounds produced were, in every case, equal in weight to the combining elements.

Dr. Priestley was a firm believer in phlogiston, and named the new element of the atmosphere which he had discovered, dephlogisticated air. He made but little use of weighing in his researches, and was not qualified by his training to go on and reap the full scientific advantages to which his great discovery opened the way. These were secured by the French chemist Lavoisier, who named the new element oxygen, and, having by his experiments overthrown the old view, he had the largest share in establishing the oxygen theory of chemistry which took its place. As Dr. Whewell observes; "Few revolutions in science have immediately excited so much general notice as the introduction of the theory of oxygen. The simplicity and symmetry of the modes of combination which it assumed, and, above all, the construction and universal adoption of a nomenclature which applied to all substances, and which seemed to reveal their inmost constitution by their name, naturally gave it an almost irresistible sway over men's minds."

But, while the theory of oxygen has guided the development of chemistry for the past hundred years, it is now following the fate of its predecessor: the facts have outgrown it, and a "New Chemistry "has arisen in its place. Yet, whatever may be the vicissitudes of theory, oxygen is still in the field—still the object of wonderful interest, and no possible changes in the future can ever dim the lustre of its discovery.

of the most distinguished chemists of the country have united in a call to all interested to convene at Northumberland, Pa., on the 1st of August, where Dr. Priestley lies entombed, to celebrate the one hundredth anniversary of his discovery of oxygen gas. Such a tribute will be most proper and befitting to his memory, and will suggest interesting phases of thought that cannot fail to make the occasion profitable to all who participate in it. In the circular of invitation it is said: "The fact that this illustrious man spent the last years of his fruitful life in this country, renders the recognition of his work by American chemists peculiarly appropriate;" and it may be added that the circumstances which brought him here, and which pertain both to his own character and the condition of his native country, are matters especially suitable for consideration at such a time. For Dr. Priestley was more than an eminent scientific discoverer—he was a sincere, courageous, high-minded man, and stood forth as the unflinching champion of liberal opinion when his country was given over to the narrow spirit of fanatical bigotry. Dr. Priestley's career exhibits the sublime moral spectacle of a man against a nation, and that, too, on a vital question of constitutional rights; and such was the conduct of the two parties, as, in the language of Dr. Thomson, to "fix an indelible disgrace upon the country," while Dr. Priestley's course will