Obituary Notices. 
499 
the principle of varying action in dynamics, and the inventor of 
the captivatingly ingenious and beautiful method of quaternions 
in Mathematics. It gave him six years of good duty in Queen’s 
College, well done, in teaching Mathematics ; and for some time 
also Natural Philosophy, in aid of his colleague Stevelly. During 
those bright years in Belfast he found his wife, and laid the 
foundation of a happiness which lasted as long as his life. 
In 1860 he was elected to succeed Forbes as Professor of 
Natural Philosophy in the University of Edinburgh. It was then 
that I became acquainted with him, and we quickly resolved to 
join in writing a book on Natural Philosophy, beginning with a 
purely geometrical preliminary chapter on Kinematics, and going 
on thence instantly to dynamics, the science of Force, as foundation 
of all that was to follow. I found him full of reverence for 
Andrews and Hamilton, and enthusiasm for science. Nothing else 
worth living for, he said ; with heart-felt sincerity I believe, 
though his life belied the saying, as no one ever was more thorough 
in public duty or more devoted to family and friends. His two 
years as “don” of Peterhouse and six of professorial gravity in 
Belfast had not wholly polished down the rough gaiety nor dulled 
in the slightest degree the cheerful humour of his student days; 
and this was a large factor in the success of our alliance for heavy 
work, in which we persevered for eighteen years. “ A merry heart 
goes all the day, Your sad, tires in a mile-a.” The making of the 
first part of “ T and T' ” was treated as a perpetual joke, in respect 
to the irksome details of interchange of drafts for “ copy,” amend- 
ments in type, and final corrections of proofs. It was lightened by 
interchange of visits between Greenhill Gardens, or Drummond 
Place, or George Square, and Largs, or Arran, or the old or new 
College of Glasgow ; but of necessity it was largely carried on by 
post. Even the postman laughed when he delivered one of our 
missives, about the size of a postage stamp, out of a pocket 
handkerchief in which he had tied it, to make sure of not dropping 
it on the way. 
One of Tait’s humours was writing in charcoal on the bare 
plaster wall of his study in Greenhill Gardens a great , table of 
living scientific worthies in order of merit . Plamilton, Faraday, 
Andrews, Stokes, and Joule headed the column, if I remember 
