Sir William Thomson printed tables for facilitating the calculations in the use of Sumner's method, and continually used them in his own voyages. He was well versed in seamanship of all kinds, and used his experience habitually to throw light on abstruse problems of dynamics. Some of these will be found in "Thomson and Tait"; for instance, in Part I, § 325, where a number of nautical phenomena are cited in illustration of an important principle of hydrodynamics. The fifth example stated is as follows: "In a smooth sea, with moderate wind blowing parallel to the shore, a sailing ship heading towards the shore, with not enough of sail set, can only be saved from creeping ashore by setting more sail, and sailing rapidly towards the shore, or the danger that is to be avoided, so as to allow her to be steered away from it. The risk of going ashore in fulfilment of Lagrange's equations is a frequent incident of 'getting under way' while lifting anchor or even after slipping from moorings." His seamanship was well known to shipmasters, with whom he had much intercourse, and whose intelligence and practical skill he held in very high regard. CHAPTER XVI LORD KELVIN IN HIS CLASS-ROOM AND LABORATORY It is impossible to convey to those who never studied at Glasgow any clear conception of Thomson as he appeared to students whom he met daily during the session. His appearance at meetings of the British Association, and his vivacious questionings of the various authors of papers, his absorption in his subject and oblivion to the flight of time when he read a paper himself, will long be remembered by scientific men: but though they suffice to suggest what he was like in his own lecture-room, the picture lacks the setting of furniture, apparatus, assistants, and students, which all contributed to the unique impression made by his personality on his pupils. The lecture-table--with long straight front and ends refracted inward, flanked by higher small round tables supported on cylindrical pillars--laden with instruments; the painted diagrams of the solar spectrum and of the paths of coloured rays through a prism, hung round the walls; the long wire with the cylindrical vibrator attached, for experiments on torsion, and the triple spiral spring vibrator, which hung at the two ends of the long blackboard; the pendulum thirty feet long, consisting of a steel wire and a twelve-pound cannon-ball as bob, suspended from the apex of the dome-roof above the lecture-table; the large iron wheel in the beautiful oriel window on the right of the lecturer, and the collection of optical instruments on the table in front of the central window spaces, from which the small iron-framed panes--dear to the heart of the architect--had been removed; the clock on either side of the room, one motionless, the other indicating the time, and having attached to it the alarm which showed when the "angry bell" outside had ceased to toll; the