The great French scientist Antoine Laurent Lavoisier was the most important figure in the development of chemistry. At the time of his birth, in Paris, in 1743, the science of chemistry lagged far behind physics, mathematics, and astronomy. Large numbers of individual facts had been discovered by chemists, but there was no adequate theoretical framework in which to fit these isolated bits of information. At that time, it was incorrectly believed that air and water were elementry substances. Worse still, there was a complete misunderstanding of the nature of fire. It was believed that all combustible materials contained a hypothtical substance called "phlogiston", and that during combustion the inflammable substance released its phlogiston into the air. In the interval from 1754 to 1774, talented chemists such as Josepth Black, Josepth Priestly, Henry Cavendish, and others had isolated such important gases as oxygen, hydrogen, nitrogen, and carbon dioxide. However, since these men accepted the phlogiston theory, they were quite unable to understand the nature or significance of the chemical substances they had discovered. Oxygen, for example, was refered to as dephlogisticated air, i.e., air from which all the phlogiston had been removed. (It was known that a silver of wood burned better in oxygen than in ordinary air; presumably, this was because dephlogisticated air could more readily absorb phlogiston from the burning wood.) Obviously, real progress in chemistry could not be made until the fundamentals were correctly understood. It was Lavoisier who managed to put the pieces of the puzzle together correctly, and to get chemical theory started on the correct path. In the first place, Lavoisier said, the phlogiston theory is completely incorrect: there is no such substance as phlogiston. The process of combustion consists of the chemical combination of the burning substances with oxygen. In the second place, water is not an elementary substance at all but a chemical compound of oxygen and hydrogen. Air is not an elementry substance either, but consists primarily of a mixture of the two gases, oxygen and nitrogen. All of these statements seem quite obvious today. Even after Lavoisier formulated his theories and presented the evidence for them, many leading chemists refused to accept his ideas. But Lavoisier's excellent textbook, Elements of Chemistry (1789), so clearly presented his hypotheses, and so convincingly marshalled the evidence in their behalf, that the younger generation of chemists was quickly convinced. Lavoisier also made some minor contributions to the study of geology, and a major contribution in the field of physiology. Like quite a few other persons on this list, Lavoisier studied law as a young man. Although he received a law degree and was admitted to the French bar, Lavoisier never practiced law. He did, though, engage in much administrative work and public service. He was active in the French Royal Acadamy of Sciences. He was also a member of the Ferme Generale, an organization involved in the collection of taxes. As a consequence, after the French Revolution in 1789, the Revolutinary government was very suspicious of him. Eventually, he was arrested, along with twenty-seven other members of the Ferme Generale. Revolutionary justice may not have been too accurate, but it was certainly speedy. On a single day (May 8, 1794), all of the twenty-eight persons were tried, convicted, and guillotined. Lavoisier was survived by his wife, a brilliant woman who had assisted him in his researches. At the trial, an appeal was made to spare Lavoisier, citing his numerous services to his country and science. The judge rejected the plea with the curt remark that, "The Republic has no need of geniuses." Somewhat closer to the truth was the remark of his colleague, the great mathematician Lagrange: "It took but a moment to sever that head, though a hundred years may not produce another like it".