Obituary Notices. 
501 
statement of the foundations of dynamical science. It is Tait’s 
last published work, primarily intended as a help to medical 
students attending his special three months’ course of lectures for 
them on Natural Philosophy. 
In the Royal Society of Edinburgh we all know something of 
how Tait has enriched its Proceedings and Transactions by his 
interesting and varied papers on mathematical and physical 
subjects from year to year since 1860, when he came to Edinburgh 
to succeed Forbes as Professor of Natural Philosophy in the 
University. Nearly all of these are now collected, along with a con- 
siderable number of other scientific papers which he brought out 
through other channels, arranged in order of time, from 1859 to 
1898; one hundred and thirty-three articles in all; republished 
by the Cambridge University Press in two splendid quarto volumes 
of 500 pages each ; a worthy memorial of a life of laborious whole- 
hearted devotion to science. 
The “ Scientific Papers ” collected in these two volumes abound in 
matter of permanent scientific interest ; and literary interest too, 
as witness the short articles on “ Hamilton,” “ Macquorne 
Rankine,” “ Balfour Stewart,” “Clerk Maxwell,” and “The 
Teaching of Natural Philosophy.” Of all the mathematical papers 
in the collection, one of those which seem to me most fundamentally 
important is Part IV. of “ Foundations of the Kinetic Theory of 
Gases,” in which we find the first proof (and, I believe, the only 
proof hitherto given) of the theorem enunciated first by Waterston 
and twelve years later independently by Clerk Maxwell, asserting 
equal average partition of energy between two sets of masses larger 
and smaller, taken as hard globes to represent the molecules of two 
different gases thoroughly mixed together. The collection contains 
also papers describing valuable experimental researches made by 
Tait through many years on various subjects : Thermo-electricity ; 
Thermal Conductivity of Metals ; Impact and Duration of Impact ; 
Pressure Errors of the Challenger thermometers ; Compressibility 
of Water, Glass, and Mercury (contributed originally to the 
“ Physics and Chemistry ” of H.M.S. Challenger). His work for 
the Challenger Report was a splendid series of very difficult 
experimental researches carried on for about nine years (1879 to 
1888), with admirable scientific inventiveness, and no less admirable 
