1920-21.] 
Obituary Notices. 
177 
John Aitken, LL.D., F.R.S. By C. G. Knott, D.Sc., LL.D., F.R.S. 
(Read January 10, 1921.) 
John Aitken, born at Falkirk on September 18, 1839, was the fourth son 
of Henry Aitken of Darroch, Falkirk, head of a well-known legal firm 
in that town. He was educated at the Falkirk Grammar School and the 
University of Glasgow, where he studied with a view to a career as an 
engineer. Two years of his apprenticeship he served in Dundee, and three 
years with Messrs Napier & Sons, shipbuilders, Glasgow. After finishing 
his apprenticeship as a marine engineer he broke down in health, and was 
compelled to abandon all thought of carrying out his profession. Thence- 
forward his interest lay in the line of scientific and especially physical 
research, for which he received a great inspiration while attending Lord 
Kelvins (then Sir William Thomson’s) classes in natural philosophy. 
His early training as an engineer was of incalculable value all through 
the long series of physical investigations which made his name famous in 
the ranks of experimenters. Most of the apparatus used in his researches 
was not only devised by him but constructed with his own hand. The 
drawing-room of the house he occupied latterly in Falkirk was transformed 
into a laboratory and workshop, with a fine turning-lathe placed in front 
of the window and supplied with all kinds of tools of the most approved 
pattern. A carpenter’s bench and work-tables laden with glass-work, blow- 
pipes, and many odds and ends of apparatus in the course of construction 
or of apparatus which had served its purpose, covered the floor space, while 
cabinets along the walls contained drawers full of thermometers and other 
delicate meteorological instruments. 
The earliest line of work which brought out his experimental skill was 
a discussion of colour sensations in a paper read before the Royal Scottish 
Societ}^ of Arts in 1872. He devised new methods of experimenting, and 
elaborated a modified form of Young’s three-colour theory of sensation, 
supporting it by means of many ingenious experiments. Another early 
line of thought led him to discuss the conditions of boiling of liquids and 
condensation of vapours, which he showed to depend on the presence of 
free surfaces separating different states ; and it was by following up some 
of the ideas suggested by this work that he hit upon what will probably 
be regarded as his greatest contribution to physical science. This was the 
demonstration that water vapour in the atmosphere will not condense to 
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