148 YOUNG. 



and for which he was well qualified by his knowledge of the prin- 

 cipal languages of Europe. 



In 1804 he married Eliza, the daughter of James Primrose Max- 

 well, of Cavendish Square, and this union is said to have been 

 attended with uninterrupted happiness ; his wife who survived him 

 left no children. 



In 1807 appeared his most elaborate and valuable work, ' A Course 

 of Lectures on Natural Philosophy and the Mechanical Arts,' being 

 the embodiment of the sixty lectures delivered while at the Royal 

 Institution, together with the labour of three more years occupied 

 in further arranging and improving them. This work comprises a 

 complete system of natural and mechanical philosophy, drawn from 

 original sources, and is distinguished not only by the extent of its 

 learning and the accuracy of its statements, but by the beauty and 

 originality of the theoretical principles. It also contains a disqui- 

 sition upon the doctrine of interference in the undulatory theory of 

 light mentioned before, the general law of which he thus enunciates : 

 " When two undulations from different origins coincide, either per- 

 fectly or very nearly in direction, their joint effect is a combination 

 of the motions belonging to each."* Sir John Herschel, speaking 

 of this discovery, says that it alone " would have sufficed to have 

 placed its author in the highest rank of scientific immortality, even 

 were his other almost innumerable claims to such a distinction dis- 

 regarded." Amongst other laborious and difficult matters of in- 

 vestigation, Dr. Young made the first and most important steps in 

 reading the Egyptian Hieroglyphics, in which he preceded Cham- 

 pollion ; and he afterwards, in 1823, published a work on this 

 subject, under the title of ' An Account of some recent Discoveries 

 in Hieroglyphical Literature and Egyptian Antiquities ; including 

 the author's original Alphabet as extended by Mr. Champollion ; 

 with a Translation of five unpublished Greek and Egyptian Manu- 

 scripts.' In the year 1808 Dr. Young was admitted a fellow of the 

 College of Physicians, and in 1810 was elected physician to St. 

 George's Hospital, a situation which he retained for the remainder 

 of his life. In 1813 he published ' An Introduction to Medical 

 Literature, including a system of practical Nosology intended as a 

 guide to Students and as an Assistant to Practitioners.' In 1816 

 Dr. Young was appointed Secretary to the Commission empowered 

 to ascertain the length of the second's pendulum, and thereby 

 establish an uniform system of weights and measures. Two years 

 subsequent to this he became secretary to the Board of Longitude, 

 and on the dissolution of that body, became sole conductor of the 

 ' Nautical Almanac.' Dr. Young at various times contributed 

 eighteen articles to the ' Quarterly Review,' of which nine were on 

 scientific subjects the rest on medicine, languages, and criticism. 



* Life of Thomas Young, M.D., <&c., by George Peacock, page 143. 



