of Edinburgh, Session 1878-79. 
409 
continued services as their Secretary, and I return my warmest 
tlianks for the communication which you have transmitted to me. 
“Be so good as convey my kind acknowledgment to the 
President and Fellows of the Royal Society. — I am, your obedient 
servant, 
“ J. H. Balfour.” 
Monday, 2 d February 1880. 
Professor DOUGLAS MACLAGAN, Vice-President, 
in the Chair. 
The following Communications were read : — 
1. On the Distribution of Temperature under the Ice in 
Frozen Lakes. By John Aitken. 
In January and February 1879 Mr J. Y. Buchanan communicated 
to this society two papers, on the distribution of temperature under 
the ice in Linlithgow Loch. In these papers he gives a most 
interesting and valuable series of temperature observations made by 
him, of the water, at different points, and at different depths, in the 
loch while it was covered with ice. He also gives the temperatures 
as taken by him under similar circumstances in Loch Lomond. 
These observations by Mr Buchanan disclose a somewhat unexpected 
thermal condition of the water. 
As water attains its maximum density at a temperature of 39 '2° 
Fahr., it has generally been supposed that water in lakes ought 
never to fall below this temperature, except near the surface. 
Because when the water is cooled below 39*2° it will float over the 
hotter and denser water, and tend to keep the surface, while the 
latter water will tend to keep the bottom, and radiation and con- 
duction will only enable a lower temperature than 39-2° to penetrate 
below the surface, yery slowly, and to a very small depth. These 
theoretical expectations are, however, entirely upset by Mr Buchanan’s 
temperature observations. He found that the greater part of the 
