106 Proceedings of the Royal Society of Edinburgh. [Sess. 
and confirm the opinion I have previously expressed,* that the discontinuity 
makes its appearance whenever there is no further gain of heat. During 
the time covered by the observations given in Table IV. the winds were 
light and variable, and this may have favoured the formation of the dis- 
continuity. The bottom temperature remained about 46 '0° until the end of 
June, and during the month of July there was a gradual and fairly con- 
tinuous rise to 46’5°, with moderate and variable winds. On 6th September, 
when an isolated observation was made, the temperature at the bottom was 
47*0°, showing that the gradual rise in bottom temperature was continued. 
The rise in bottom temperature after the formation of the discontinuity is 
very gradual, whereas before its formation changes in bottom temperature 
took place by small leaps following high winds. This gradual rise is prob- 
ably due to the very slow currents which I believe to exist at the bottom 
of stratified lakes, and also to convection currents started by the tempera- 
ture seiche. It also indicates that after the formation of the discontinuity 
layer in a lake the direct return currents take place above the discontinuity. 
Otherwise there would still be spasmodic increases of temperature follow- 
ing high winds. 
It is unfortunate that I was unable to continue my observations on into 
the autumn, for though the discontinuity made its appearance during the 
cold weather of June, it did not become very distinct, and was masked 
somewhat by the warmer weather of July which followed. That the dis- 
continuity did become more marked in the autumn is shown by an 
observation which I caused to be taken on 6th September, which shows a 
steep temperature gradient between 75 and 85 feet (see Table V.). 
Table V. 
Temperature on Loch Garry , 6th September 1908. 
Surface 
54-0° 
25 feet 
53-8 
60 „ 
53 7 
70 „ 
52*4 
75 „ 
51*2 
80 „ 
50-0 
85 „ 
48-0 
100 „ 
473 
150 „ 
47-0 
200 „ 
47-0 
Observations made in August and September would probably have given 
good examples of the temperature seiche. As it was, hourly or two-hourly 
* Proc. R.S.E . , vol. xxviii. p. 7. 
