LORD KELVIN 93 



brain so much above the ordinary, so much more rapid in 

 action than the average, can be a first-rate teacher. 

 Certainly, in my own case, I gained much more in my 

 second than in my first year's attendance. But Thomson 

 never allowed the interest of his students to flag ; his 

 aptness in illustration and his vigour of language prevented 

 that. Lecturing one day on ' Couples,' he explained how 

 forces must be applied to constitute a couple, and illus- 

 trated the direction of the forces by turning round the 

 gas-bracket. This led to a discussion on the miserable 

 quality of Glasgow coal-gas, and how it might be improved. 

 Following again the main idea, he caught hold of the 

 door, and swung it to and fro ; but, again, his mind 

 diverged to the difference in the structure of English and 

 Scottish doors. We never forgot what a couple was ; but 

 the idea might have been conveyed more succinctly. 

 He held strong views on the 'absurd, ridiculous, time- 

 wasting, soul-destroying system of British weights and 

 measures ' ; and in spite of all the efforts of the ' Decimal 

 Association,' we, the Americans, and the Russians remain 

 examples of irrational conservatism in respect of the 

 awkwardness of our systems. 



The Cartesian method of locating a point was indelibly 

 impressed on my memory by the following incident: A 

 student, whose position was roughly about the centre of 

 the lecture-room, made that noise so disturbing to a 

 lecturer, yet so difficult to locate, caused by gently rubbing 

 the sole of his foot on the floor. ' Mr. Macfarlane ! ' said 

 Sir William. Mr. Macfarlane, the fides Achates, came, 

 received a whispered communication, and went out of the 

 room. In about ten minutes he returned with a tape-line, 

 and proceeded to measure a length along one wall, on 

 which he made a pencil-mark. He then measured out at 

 right angles another length, and made a chalk-mark on 

 the floor, erecting on it a pointer. ' Mr. Smith, it was you 



