Obituary Notices. 
503 
believe, had truly attributed this fact to the blackened side being 
rendered somewhat warmer by the light ; but none before Tait 
and Dewar had ever imagined the dynamical cause, — the largeness 
of the free path of the molecule of the highly rarefied air, and the 
greater average velocity of rebound of the molecules from the 
warmer side. Long free path was the open sesame to the mystery. 
The Keith Medal of the Koyal Society of Edinburgh was 
awarded to Professor Tait in the year 1869, and again in 1874; 
and one of the Royal Medals of the Royal Society of London was 
awarded to him in the year 1886. The Gunning Victoria Jubilee 
Prize of the Royal Society of Edinburgh was awarded to him in 
1890. 
Enthusiast as he was in experimental and mathematical work, 
he never allowed this to interfere with his University teaching, to 
which, from beginning to end of the forty years of his Professorship, 
he devoted himself with ever fresh vigour, and with unremitting 
faithfulness, as his primary public duty. How happily and use- 
fully and inspiringly he performed it, has been remembered with 
gratitude by all who have ever had the privilege of being students 
in his class. 
With not less devotion and faithfulness during all these years 
he has worked for the Royal Society, of which he was elected a 
Eellow when he came to Edinburgh as Professor. At the com- 
mencement of the following session he was elected a Member of 
Council; and in 1864 he became one of the Secretaries to the 
ordinary meetings. In 1879, in succession to Professor Balfour, 
he was elected to the General Secretaryship; and he held this 
office till the end of his life. 
His loss will be felt in the Society, not only as an active partici- 
pator in its scientific work, but also as a wise counsellor and guide. 
It has been put on record that “ The Council always felt that in 
“ his hands the affairs of the Society were safe, that nothing would 
“ be forgotten, and that everything that ought to be done would be 
“ brought before it at the right time and in the right way.” In 
words that have already been used by the Council, I desire now to 
say on the part, not only of the Council, but of all who have 
known Tait personally, and of a largely wider circle of scientific 
men who know his works, — “We all feel that a great man has 
