SIR WILLIAM THOMSON 31 



regularity ; and on the morning following the Monday evening meetings 

 paid a visit to Tail's Laboratory immediately after the conclusion of Tail's 

 lecture. It was then that we laboratory "veterans" had an opportunity 

 of coming into closer touch with the great Natural Philosopher, who 

 would occasionally pass round the laboratory and inspect the experiments 

 which were in progress. Most instructive discussions would at times 

 arise, Kelvin's mind branching off into some line of thought suggested 

 by, but not really intimately connected with, the experiment. At other 

 times the conversation between Kelvin and Tait turned on the papers 

 which had been communicated the evening before. I remember a lively 

 discussion arising on the statistical effect of light impressions on the 

 eye. The argument was reminiscent of the old tale of the two knights 

 and the shield; for while Tait was laying stress on the time average, 

 Thomson was looking at it from the point of view of the space average. 



For many years Tail's successive assistants reported the Meetings of 

 the Royal Society to Nature ; and this duty fell to me during the years 

 1879-83. Al one of these meetings Sir William, as he then was, had in 

 his well-known discursive but infinitely suggestive manner so talked round 

 the subject of the communicalion lhat I had some difficulty in quite under- 

 standing its real essence. Next morning I tried to get enlightenment from 

 Tait. He laughed and said " I had rather not risk it ; but the great man is 

 coming at twelve better tackle him himself." When in due time Sir William 

 was "tackled," he fixed his gaze at infinity for a few moments and then, 

 a happy thought striking him, he said, with a quick gesture betokening 

 release from burden, " Oh, I'll tell you what you should do. Just wait till 

 the Nature Report is published that fellow always reports me well." Tail's 

 merriment was immense as he unfolded the situation, and he chaffed 

 Thomson as to his obvious inability to explain his own meaning. Not a 

 few of both Kelvin's and Tail's communications to the Royal Society of 

 Edinburgh were never writlen oul by ihem ; ihey appear as reporls only 

 in the columns of Nature. 



Anolher scene, in which Thomson and Tail were the main agenls, rises 

 in the memory. Once on a Saturday morning in summer when two of 

 us were working with electromeler and galvanomeler in ihe Class room 

 Tait arrived in some excitement and said " Thomson will be here in half 

 an hour on his way to London. He wishes to try some experiments with 

 our Gramme machine and will need your cooperation wilh electrometer 



