In the _Encyclopaedia Britannica_, Sir William has published an article describing the instruments--chiefly invented by himself--which were used in laying the Atlantic Cable. In the same contribution he describes the expeditions undertaken in 1857 and 1858 for the purpose of laying the Atlantic Cable, and the difficulties that had to be encountered in that great enterprise. This he was eminently qualified to do from his experience as acting electrician on board the _Agamemnon_ during the progress of the work which resulted in the completion, in August, 1858, of the Atlantic Cable, and the astonishment of the world at finding the two opposite shores of the great ocean placed in instantaneous communication with each other. For some time after the cable was laid he remained at Valentia, endeavouring to bring his galvanometer to still greater perfection. From the subsequent failure of the Atlantic Cable, and until it was finally established as a successful "institution," Sir William was busily employed in seeking to make more perfect and easy the difficult science of submarine telegraphy; and in the expeditions of 1865 and 1866, which he accompanied, his counsel and assistance proved of inestimable value. From the Royal Society of Edinburgh Sir William received the Keith Prize for the years 1862 and 1863. On the occasion of the award, Sir David Brewster, the Vice-President of the Society, thus referred to the many valuable papers he had communicated to the Society during the seventeen years of his connection with it:--"These papers, and others elsewhere published, relate principally to the theories of Electricity, Magnetism, and Heat, and evince a genius for the mathematical treatment of physical questions which has not been surpassed, if equalled, by that of any living philosopher. In studying the mathematical theory of Electricity, he has greatly extended the general theorems demonstrated by our distinguished countryman, Mr. Green; and was led to the principle of 'electrical images,' by which he was enabled to solve many problems respecting the distribution of electricity on conductors, which had been regarded as insoluble by the most eminent mathematicians in Europe. In his researches on Thermo-dynamics, Professor Thomson has been equally successful. In his papers 'On the Dynamical Theory of Heat,' he has applied the fundamental propositions of the theory to bodies of all kinds, and he has adduced many curious and important results regarding the specific heats of bodies, which have been completely verified by the accurate experiments of M. Joule. No less important are Professor Thomson's researches on Solar Heat, contained in his remarkable papers 'On the Mechanical Energy of the Solar System;' his researches on the Conservation of Energy, as applied to organic as well as inorganic processes; and his fine theory of the dissipation of Energy, as given in his paper 'On a Universal Tendency in Nature to the Dissipation of