416 
Proceedings of the Royal Society 
vations quoted in this paper, and by all the observations which I 
have been able to make in other lakes, namely, that at any one 
date, especially during the warm half of the year, the isothermal 
surfaces, even at depths where there is no rapid change of tempera- 
ture, are not planes, hut have many curvatures and unevennesses. 
These unevennesses are particularly accentuated in the region of 
most rapid change of temperatures or on the steepest gradient of the 
temperature curve. Here the movements of the thermometer a few 
yards in a horizontal direction may place it in water of very dif- 
ferent temperature. On both days a fresh breeze was blowing, and,, 
though it was possible to keep station very satisfactorily from a 
nautical point of view, the station kept was an average one — that is, 
instead of being a point, it was an area, and an area perhaps 20 to 
30 yards long by 10 to 20 yards wide. The investigation of the 
body of water having the steepest temperature gradient is very 
interesting, hut it should he attempted only under the most favour- 
able circumstances — either the weather should he perfectly calm, or 
the boat should be anchored. In future work the minute delinea- 
tion of the steepest part of the temperature gradient should have 
an important place. 
Table YII. — Observations in Loch Lomond , 14 th November 1885. 
Name of Basin, 
Luss. 
Tarbet. 
Locality, 
| Boss Island. 
Inversnaid. 
Miles from Balloch Pier, 
Depth at Station, . 
Hour of day, . 
No. of Station, 
7 
i 34 
1 3 P.M. 
16 
14 
100 
1 P.M. 
17 
Depth. 1 
Fathoms. 
No. of 
Thermo- 
meter. 
j Temperature (Fahr. ). 
0 
10 
20 
l 30 
( 30 
40 
50 
65 
84 
100 
1 
Negretti’s 
no® overturning 
Thermo- 
meters. 
46-6 
46-3 
46-3 
46-3 
46°0 
45‘8 
45’8- 
44*3 ) 
44-2 \ 
42-3 
42-2 
42-15 
42-1 
42-1 
