Watt had divined the import of Priestley's experiment, for he had mastered all knowledge bearing upon the question, but even when this was communicated to Priestley, he could not accept it, and, after making new experiments, he writes Watt, April 29, 1783, "Behold with surprise and indignation the figure of an apparatus that has utterly ruined your beautiful hypothesis," giving a rough sketch with his pen of the apparatus employed. Mark the promptitude of the master who had deciphered the message which the experimenter himself could not translate. He immediately writes in reply May 2, 1783: I deny that your experiment ruins my hypothesis. It is not founded on so brittle a basis as an earthen retort, nor on _its_ converting water into air. I founded it on the other facts, and was obliged to stretch it a good deal before it would fit this experiment.... I maintain my hypothesis until it shall be shown that the water formed after the explosion of the pure and inflammable airs, has some other origin. He also writes to Mr. DeLuc on May 18th: I do not see Dr. Priestley's experiment in the same light that he does. It does not disprove my theory.... My assertion was simply, that air (_i.e._, dephlogisticated air, or oxygen, which was also commonly called vital air, pure air, or simple _air_) was water deprived of its phlogiston, and united to heat, which I grounded on the decomposition of air by inflammation with inflammable air, the residuum, or product of which, is only water and heat. Having, by experiments of his own, fully satisfied himself of the correctness of his theory, in November he prepared a full statement for the Royal Society, having asked the society to withhold his first paper until he could prove it for himself by experiment. He never doubted its correctness, but some members of the society advised that it had better be supported by facts. When the discovery was so daring that Priestley, who made the experiments, could not believe it and had to be convinced by Watt of its correctness, there seems little room left for other claimants, nor for doubt as to whom is due the credit of the revelation. Watt encountered the difficulties of different weights and measures in his studies of foreign writers upon chemistry, a serious inconvenience which still remains with us. He wrote Mr. Kirwan, November, 1783: