The chief discoveries relating to auscultation were undoubtedly Laennec’s; yet his knowledge of acoustics was by no means profound, and he was often not successful in explaining rationally the sounds that he heard in the chest. Dr. Williams soon started in the path of applying acoustic laws in this field, and in 1828 he produced his valuable “Rational Exposition of the Physical Signs of Diseases of the Chest,” suggesting various improvements in the construction and use of stethoscopes. Returning to London, Dr. Williams derived great benefits through an introduction to Dr. (afterwards Sir James) Clark, so long attached as physician to the Queen, and from the family acquaintance with Lord Heytesbury. His work above mentioned was favourably reviewed, and soon made its way; and many of his explanations are accepted to the present day. After various travels with patients, he settled in Half Moon Street, Piccadilly, in 1830, having married his cousin, Miss Harriett Jenkins, of Chepstow. Becoming a member of the Royal Institution, Dr. Williams was introduced to Faraday, and was soon engaged to write for the “Cyclopædia of Practical Medicine,” to which he contributed numerous valuable articles on auscultation and diseases of the chest. In these articles he recommended strongly the cure of catarrh by the heroic process of reducing the supply of fluid. The remedial uses of counter-irritation were carefully expounded: and dyspnœa, difficult or distressed breathing, was clearly described. In 1833, while practice grew but slowly, the second edition of the Rational Exposition was brought out, containing an enlarged section on the sounds of the heart in health and disease. For some years Dr. Williams had considered the questions involved, and by experimental inquiries in 1835 he established that several causes to which they had hitherto been ascribed could not be the cause of the sounds of the heart, and that the first sound was produced by the muscular contraction of the ventricles, and the second by the reaction of the arterial blood tightening the semilunar valves. His anticipation by Rouanet in 1832 in the latter point has, however, been more recently made evident. A third edition of his book, now of increased importance, was published in 1835, under the title of “The Pathology and Diagnosis of Diseases of the Chest, illustrated especially by a Rational Exposition of their Physical Signs.” It was reprinted in America, and translated into German and Swedish. The same year he was elected F.R.S.