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362 sect. He spent much time at parties, both grave and gay; went frequently to the theatre in spite of the remonstrances of his friends, took private lessons in dancing and in playing on the flute."

After prosecuting his medical studies in Edinburgh, he made a thorough tour of Scotland at the close of the session of 1795, and returning to England went at once to Göttingen, "where, along with his medical studies, he took lessons in drawing, dancing, riding, and music, in all of which he made rapid progress. He was passionately fond of horsemanship, and there were no feats in that art too daring for him to accomplish."

In 1797 his uncle, Dr. Brocklesby, died, leaving him his house, library, collection of prints and pictures, and fifty thousand dollars in money, which enabled him to pursue his inquiries with greater facility, and in the beginning of 1800 he commenced the practice of medicine in London. In 1801 he was appointed Professor of Natural Philosophy in the Royal Institution of Great Britain, and he conducted its journal along with Humphrey Davy, then Professor of Chemistry. The first year he gave thirty-one lectures, and afterward sixty, which were published in 1807, in two quarto volumes, under the title of "A Course of Lectures on Natural Philosophy and the Mechanical Arts," a work which, notwithstanding its obscurity both in language and in thought, is rich in original and ingenious views, and of inestimable value to the student of physics and the mechanic arts.

It was in May, 1801. when Dr. Young was twenty-eight years of age, that, reflecting on the experiments of Newton, he was led to the discovery of a law which "appeared to him to account for a greater variety of interesting phenomena than any other optical principle that had yet been made known." This was the law of the Interference of Light, which he explained on the principle of the undulatory theory. This theory had been long before propounded by Huyghens and Hooke, but Dr. Young revived it, gave it greater precision of form, and first proved that it accounts for luminous phenomena which can be explained by no other known hypothesis. His views were developed in Nicholson's Journal for 1801, in the following propositions: