Watt's chemical studies in 1783, and the calculations they involved from experiments made by foreign chemists, induced him to make a proposal for a philosophical _uniformity of weights and measures_; and he discussed this proposal with Priestley and Magellan. While Watt was examining the constituent parts of water, he had opportunities of familiar intercourse not only with Priestley, but with Withering, Keir, Edgeworth, Galton, Darwin, and his own partner, Boulton--all men above the average for their common interest in scientific inquiries. Dr. Parr frequently attended their meetings, and they kept up a correspondence with Sir William Herschel, Sir Joseph Banks, Dr. Solander, and Afzelius. Mrs. Schimmelpenninck, who was greatly given to physiognomical studies, has left us this picture of Watt at this period. "Mr. Boulton was a man to rule society with dignity; Mr. Watt, to lead the contemplative life of a deeply introverted and patiently observant philosopher. He was one of the most complete specimens of the melancholic temperament. His head was generally bent forward, or leaning on his hand in meditation; his shoulders stooping, and his chest falling in; his limbs lank and unmuscular, and his complexion sallow. His intellectual development was magnificent; comparison and causality immense, with large ideality and constructiveness, individuality, an enormous concentrativeness and caution. "He had a broad Scottish accent; gentle, modest, and unassuming manners; yet, when he entered a room, men of letters, men of science, nay, military men, artists, ladies, even little children, thronged round him. Ladies would appeal to him on the best means of devising grates, curing smoky chimneys, warming their houses, and obtaining fast colors. I can speak from experience of his teaching me how to make a dulcimer and improve a Jew's harp." In the year 1786, Watt and Boulton visited Paris, on the invitation of the French Government, to superintend the erection of certain steam-engines, and especially to suggest improvements in the great hydraulic machine of Marly, which Watt himself designates a "venerable" work. In Paris Watt made many acquaintances, including Lavoisier, Laplace, Fourcroy, and others scarcely less eminent; and while here he discussed with Berthollet a new method of _bleaching_ by chlorides, an invention of the latter which Watt subsequently introduced into England.