TEMPERATURE OF SCOTTISH LAKES 
143 
The importance of viscosity of water has not hitherto been con- 
sidered in relation to lake temperatures, but it is a well-established 
fact that the viscosity of water at 25° C. is only about one-half that 
of water at 0° C. Biologists have recognised the importance of this 
in regulating the forms and disposition of plankton animals. It seems 
likely that this change of viscosity with temperature is equally im- 
portant in the circulation of lakes. Whenever there is a discontinuity 
in temperature there is a mobile liquid resting on a relatively viscous 
liquid. The tendency of this must be to confine wind-produced 
currents to water above the discontinuity, and so to strengthen the 
effect of the difference in density between the upper and lower layers 
of water. The difference in viscosity may, in fact, be as important as 
the difference in density in determining the circulation. 
While we are in the region of speculation, I may be permitted 
further to suggest that there is an analogy between the temperature 
seiche in lakes and the movements in the upper air. There again we 
have two layers of different density one above the other, and the rapid 
changes in temperature at great heights may be due to causes similar 
to those which produce large variations of temperature in the neigh- 
bourhood of the discontinuity layer in lakes. 
BIBLIOGRAPHY 
The following is a list of papers dealing with the fresh-water lakes of 
Scotland. There is also a considerable literature dealing with salt-water 
lakes^ but as the conditions in salt-water basins are quite different from 
the conditions in fresh-water basins^ I have restricted the bibliography to 
the fresh-water lakes. The chief contributions to the study of the 
temperature of salt-water basins have been made by Sir John Murray 
and Dr H. R. Mill. 
In addition to the following papers^ reference should be made to the 
various Lake Survey Reports. 
1838. Leslie^ John,, Treatises on Various Subjects of Natural and Chemical 
Philosophy, p. 28 L 
Leslie, John, article " Chmate/' Eighth Edition^ Encycl. Brit., 
vol. vi. p. 777. 
187L Buchan^ Alexander^ Remarks on the Deep-water Temperature 
of Lochs Lomond, Katrine^ and Tay," Proc. Roy. Soc. Edin., 
vol. vii. p. 79 L (Gives Jardine's observations in Lochs Lomond^, 
Katrine, and Tay.) 
Christison, Robert^ " Opening Address to the Royal Society of Edin- 
burgh, 1871-72," Proc. Roy. Soc. Edin., vol. vii. p. 567. (The 
author describes the existence of a discontinuity in temperature.) 
1872. Buchan, Alexander, Remarks on the Deep-water Temperatures 
of Lochs Lomond, Katrine^ and Tay," Brit. Assoc. Report, vol. 
xlii. p. 207. 
