Lord Kelvin was hearty and genial, and generally wore a winning smile; and he was the most modest of great men.
On one occasion he paid a visit with a friend to some well-known electrical works. They were escorted over the workshops by the senior foreman, a man of much intelligence and an enthusiastic electrician. Entirely unaware of his visitor's identity, he minutely explained the details of the plant and machinery, and lectured him in his rôle of layman quite professionally. Lord Kelvin's friend was on the point of interrupting several times, but an amused signal from the great master of electricity kept him silent. When the tour of inspection was complete, Lord Kelvin quietly turned to the foreman and asked, "What, then, is electricity?" This was a poser for the man, who, somewhat shamefacedly, confessed that he could not say. "Well, well," said Lord Kelvin gently, "that is the only thing about electricity which you and I do not know."
Lord Kelvin was the greatest teacher of physics of his day, but his lectures were never simple; in fact, his "popular addresses" were more suitable for wranglers than anybody else. His subjects were so simple to him that he frequently overlooked the fact that he took his audience clean out of their depth. He was essentially a teacher of teachers.
In 1896 Lord Kelvin celebrated the jubilee of his professorship at the Glasgow University, and on this occasion men of science from all parts of the world did honour to the great physicist; and he was presented with the Arago gold medal by the Académie des Sciences. Numerous addresses were presented to him from the various universities, academies, and societies of the world,
