109 
1908-9.] Temperature Observations in Loch Garry. 
observations upset the experiment. By bicycling from one end of the lake 
to the other, however, and making observations alternately at the two 
ends of the lake, rough opposition in phase was shown. A change of wind 
during this series of observations further spoilt the experiment. A rough 
calculation from the approximate formula of the period of the temperature 
seiche gives a value of the same order as the observed value. 
The important points in the Loch Garry observations may be sum- 
marised as follows : — 
1. They give a complete series of observations in a temperate lake for 
the portion of the year during which the lake is gaining heat, and are 
comparable to the observations in Loch Ness, which is a tropical lake. 
2. They show the apparently fortuitous manner in which freezing may 
take place in the larger temperate lakes. 
3. They show how strong winds have the effect of producing currents 
at considerable depths. 
4. They indicate that the formation of the discontinuity layer in a lake 
takes place whenever the surface layer begins to cool. 
5. They indicate that after the formation of the discontinuity the return 
current is not directly appreciable at the bottom of a lake. 
6. They show that the temperature seiche is not a phenomenon 
peculiar to Loch Ness or to very deep lakes; but that it is possible to have 
temperature oscillations even in small temperate lakes, and even when the 
discontinuity is not pronounced. 
The observations suggest lines on which observations in other lakes of 
moderate size may be made. As a rule, observers have contented themselves 
with observations at wide intervals of time. It is difficult to interpret 
properly such isolated observations, and they may be very misleading ; but 
when consecutive observations are made at near intervals of time the 
temperature changes can be closely followed, and a number of such series 
of observations in different lakes would be invaluable for the purpose of 
comparison. The observations in Loch Garry are given in the Appendix to 
this paper, so that they may be available for reference to other observers. 
Observations with Current Metre. 
With a view to measure directly the currents occurring in a lake, I 
procured one of Ekman’s propeller current metres.* The instrument 
* The cost of this apparatus and the necessary gear was partially defrayed by a grant 
from the Moray Bequest of the University of Edinburgh. 
