that Thomson was thinking in terms of a unitary continuum theory, whereas Descartes was thinking in terms of three different types of matter, each relating respectively to emission, transmission, and reflection of light. About 60 scientific papers were written by approximately 25 scientists. Following the lead of Thomson and Tait, the branch of topology called knot theory was developed. Kelvin's initiative in this complex study that continues to inspire new mathematics has led to persistence of the topic in history of science. Marine Thomson was an enthusiastic yachtsman, his interest in all things relating to the sea perhaps arising from, or fostered by, his experiences on the Agamemnon and the Great Eastern. Thomson introduced a method of deep-sea depth sounding, in which a steel piano wire replaces the ordinary hand line. The wire glides so easily to the bottom that "flying soundings" can be taken while the ship is at full speed. A pressure gauge to register the depth of the sinker was added by Thomson. About the same time he revived the Sumner method of finding a ship's position, and calculated a set of tables for its ready application. During the 1880s, Thomson worked to perfect the adjustable compass to correct errors arising from magnetic deviation owing to the increased use of iron in naval architecture. Thomson's design was a great improvement on the older instruments, being steadier and less hampered by friction. The deviation due to the ship's magnetism was corrected by movable iron masses at the binnacle. Thomson's innovations involved much detailed work to develop principles identified by George Biddell Airy and others, but contributed little in terms of novel physical thinking. Thomson's energetic lobbying and networking proved effective in gaining acceptance of his instrument by The Admiralty. Charles Babbage had been among the first to suggest that a lighthouse might be made to signal a distinctive number by occultations of its light, but Thomson pointed out the merits of the Morse 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. Electrical standards Thomson did more than any other electrician up to his time in introducing accurate methods and apparatus for measuring electricity. As early as 1845 he pointed out that the experimental results of William Snow Harris were in accordance with the laws of Coulomb. In the Memoirs of the