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 Review, December 1888 and February 1889; New Review, 1892).

As a lecturer Tyndall was famed for the charm and animation of his language, for lucidity of exposition, and singular skill in devising and conducting beautiful experimental illustrations. As a writer he did perhaps more than any other person of his time for the diffusion of scientific knowledge. By the publication of his lectures and essays he aimed especially at rendering intelligible to all, in non-technical language, the dominant scientific ideas of the century. His work has borne abundant fruit in inciting others to take up the great interests which possessed so powerful an attraction for himself. In ‘Heat as a Mode of Motion’ (see below), which has been regarded as the best of Tyndall's books, that difficult subject was for the first time presented in a popular form. The book on ‘Light’ gives the substance of lectures delivered in the United States in the winter of 1872–3. The proceeds of these lectures, which by judicious investment amounted in a few years to between 6,000l. and 7,000l., were devoted to the encouragement of science in the United States.

His views upon the great question as to the relation between science and theological opinions are best given in his presidential address to the British Association at Belfast in 1874, which occasioned much controversy at the time (reprinted, with essays on kindred subjects, in ‘Fragments of Science,’ vol. ii.) The main purpose of that address was to maintain the claims of science to discuss all such questions fully and freely in all their bearings.

On 29 Feb. 1876 Tyndall married Louisa, eldest daughter of Lord Claud Hamilton, who became his companion in all things. In 1877 they built a cottage at Bel Alp, on the northern side of the Valais, above Brieg. There they spent their summers amid his favourite haunts. In 1885 they built what Tyndall called ‘a retreat for his old age’ upon the summit of Hind Head, on the Surrey moors, then a very retired district. Sleeplessness and weakness of digestion—ills from which he had suffered more or less all his life—increased upon him in later years, and caused him to resign his post at the Royal Institution in March 1887. His later years were for the most part spent at Hind Head. Repeated attacks of severe illness, unhappily, prevented the execution of the many plans he had laid out for his years of retirement. In 1893 he returned greatly benefited from a three months' sojourn in the Alps. But a dose of chloral, accidentally administered, brought all to a close on 4 Dec. 1893.

Tyndall's single-hearted devotion to science and indifference to worldly advantages were but one manifestation of a noble and generous nature. A resolute will and lofty principles, always pointing to a high ideal, were in him associated with great tenderness and consideration for others. His chivalrous sense of justice led him not unfrequently—irrespective of nationality or even of personal acquaintance, and often at great cost of time and trouble to himself—to take up the cause of men whom he deemed to have been unfairly treated or overlooked in respect to their scientific merits. He thus vindicated the claim of the unfortunate German physician, Dr. Julius Robert Mayer, to have been the first to lay down clearly the principle of the conservation of energy and to point out its universal application; and succeeded in obtaining his recognition by the scientific world in spite of eminent opposition. The same spirit appeared in his defence of Rendu's title to a share in the explanation of glacier movement, and of Wigham's services in regard to lighthouses.

Tyndall took a warm interest in some great political questions. He sided strongly with the liberal unionists in opposing Mr. Gladstone's home-rule policy.

Tyndall was of middle height, sparely built, but with a strength, toughness, and flexibility of limb which qualified him to endure great fatigue and achieve the most difficult feats as a mountaineer. His face was rather stern and strongly marked, but the sharp features assumed an exceedingly pleasing expression when his sympathy was touched, and the effect was heightened by the quality of his voice. His eyes were grey-blue, and his hair, light-brown in youth, was abundant and of very fine texture. He had generally, like Faraday, to bespeak a hat on account of the unusual length of his head. A medallion of Tyndall, executed by Woolner in 1876, is perhaps the best likeness that exists of him.

Tyndall's works have been translated into most European languages. In Germany (where Helmholtz and Wiedemann undertook the translations and wrote prefaces) they are read almost as much as in England. Some thousands of his books are sold yearly in America, and a few translations have been made into the languages of India, China, and Japan. In the Royal Society's catalogue of scientific papers 145 entries appear under Tyn-