362 THE POPULAR SCIENCE MONTHLY. 



sect. He spent much time at parties, both grave and gay ; went fre- 

 quently to the tlieatre in spite of the remonstrances of his friends, took 

 private lessons in dancing and in playing on tlie flute." 



After prosecuting his medical studies in Edinburgh, he made a 

 thorough tour of Scotland at the close of the session of 1T95, and re- 

 turning to England went at once to Gottingen, " where, along with 

 his medical studies, he took lessons in drawing, dancing, riding, and 

 music, in all of which he made rapid progress. He w^as 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 cf 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 Philoso- 

 phy 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 cf 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 ex- 

 plained by no other known hypothesis. His views were develojied m 

 Nicholso7i's Journal for 1801, in the following propositions : 



"I am of opinion," says he, "that hglit is probably the undulation of an 

 clastic medium, because — 



" 1. Its velocity in the same medium is always equal. 



"2. All refractions are attended Avitli a partial reflection. 



" 3. There is no reason to expect that such a vibration should diverge equal- 

 ly in all directions, and it is probable that it does diverge in a small degree in 

 every direction. 



"4. The dispersion of differently colored rays is no more incompatible with 

 this system than with the common opinion, which only assigns for it the nomi- 

 nal cause of different elective attractions. 



" 5. Reflection and refraction are equally explicable on both suppositions. 



" C). Inflection is as well, and, it may be added, even much better, explained 

 by this theory. 



