On July 8, 1799, he sent from Emmanuel College a paper to the Royal Society, entitled ‘Outlines of Experiments and Inquiries respecting Sound and Light.’ In it he established the great principle of the interference of sounds, and he wrote one section on the analogy of sound and light. In 1800 he referred, in the ‘British Magazine,’ to a young gentleman of Edinburgh ‘who certainly promises, in the course of time, to add considerably to our knowledge of the works of nature, but who had a paper in the “Philosophical Transactions” for 1798, in which what was new was not true, and what was true was not new.’ Dr. Robison, in his article on Music in the ‘Encyclopædia Britannica,’ criticised Young’s papers. In Nicholson’s ‘Philosophical Journal’ for 1801 Young answered Robison, and published an extension of the principles of interferences from sound to light. This was the preliminary announcement of his views regarding the undulatory theory of light. His first paper on the ‘Theory of Light and Colours’ was read to the Royal Society, November 12, 1801. His second paper on this subject was read July 1, 1802, and his third November 24, 1803. His ‘Syllabus of Lectures at the Royal Institution,’ dated January 19, 1802, p. 116, gives the first printed account of his views. He says, ‘Speaking of Newton’s views, it will be sufficient for our present purpose to enumerate the respective explanations of the principal phenomena of light as they are furnished by the Newtonian system, and by the theory lately submitted to the Royal Society’; and (p. 117) he says, ‘The colours of thin and of thick plates, and the fringes produced by inflection, are referred by Newton to the very complicated effects of an undulating medium on the corpuscles of light, but without any attempt to accommodate the explanations to the measures obtained from his own accurate and elegant experiments; those of striated surfaces he has not noticed. But the general law by which all these appearances are governed may be very easily deduced from the interference of two coincident undulations which either co-operate or destroy each other in the same manner as two musical notes produce an alternate intermission and remission in the beating of an imperfect unison.’ ‘The young gentleman of Edinburgh,’ afterwards known as Lord Brougham, in the ‘Edinburgh Review,’ January 1803, criticised the Royal Society papers.