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 among the Western Islands, or up the Mediterranean, or across the Atlantic to Madeira and America. His interest in all things relating to the sea perhaps arose, or at any rate was fostered, by his experiences on the Agamemnon and the Great Eastern. Babbage was among the first to suggest that a lighthouse might be made to signal a distinctive number by occultations of its light; but Sir William pointed out the merits of the Morse telegraphic code for the purpose, and urged that the signals should consist of short and long flashes of the light to represent the dots and dashes.

Sir William has done more than any other electrician to introduce accurate methods and apparatus for measuring electricity. As early as 1845 his mind was attracted to this subject. He pointed out that the experimental results of William Snow Harris were in accordance with the laws of Coulomb.

In the Memoirs of the Roman Academy of Sciences for 1857 he published a description of his new divided ring electrometer, which is based on the old electroscope of Bohnenberger and since then he has introduced a chain or series of beautiful and effective instruments, including the quadrant electrometer, which cover the entire field of electrostatic measurement. His delicate mirror galvanometer has also been the forerunner of a later circle of equally precise apparatus for the measurement of current or dynamic electricity.

To give even a brief account of all his physical researches would require a separate volume; and many of them are too abstruse or mathematical for the general reader. His varied services have been acknowledged by numerous distinctions, including the highest honour a British man of science can obtain—the Presidency of the Royal Society of London, to which he was elected at the end of last year.

Sir William Thomson has been all his life a firm