414 
Proceedings of the Boyal Society 
Table V. — Comparative Table of the Mean Temperature of certain intervals 
in the waters of the Ardlui and the Luss Basins on 5th September and 
15 th October 1885. 
Interval, . 
Surf, to 20 fms. 
Surf, to 30 fms. 
20 to 30 fms. 
Date, 
Sept. 5 
Oct. 15 
Sept. 5 
Oct. 15 
Sept. 5 
Oct. 15 
Mean Temp, at 
( Luss, 
53° -24 
49° ’12 
51°'37 
49°-00 
47° -65 
49° -00 
\ Ardlui, 
52° -90 
46°-58 
50° -33 
46° -40 
45°-85 
46° -05 
Difference, 
0°*34 
2°-54 
F-04 
2° -60 
l°-80 
2° -95 
A comparison of these data brings out very clearly the difference in 
conditions obtaining in the two basins notwithstanding their likeness 
in depth. At Ardlui the predominating influence is that of the import- 
ant tributary, the Falloch, which influences the temperature of the 
lake water in its neighbourhood most, while its temperature is lower 
than that of the lake. On 16th October the temperature of the water 
of the Douglas was 44° *6 F., while that of the surface of the lake in its 
neighbourhood was 49° # 0. On 13th November the temperature of 
the stream at Inversnaid was 40°, and that of the lake surface 46°. 
From its rise and course the Falloch is more likely to he colder than 
warmer than these streams, so that even in October it must have 
begun to spread its cooling influence over the lower waters of the 
Ardlui basin. When the water of the stream is warmer than that 
of the lake surface, it passes away with the drainage, and imparts as 
much of its heat to the atmosphere above it as to the water below. 
When its temperature is lower than that of the lake surface, and in 
all probability it is so for more than half the year, it sinks into the 
body of the lake, and imparts its cold entirely to its deeper waters. 
It is obvious then that during the time that it is colder than the 
lake, the water of the Falloch must produce a much greater effect 
on it than during the opposite season; hence the position of the 
Ardlui station, with respect to the principal tributary of the lake, 
renders it natural to expect that its waters would be colder than 
they are found to be in the Luss basin, which, from its size and 
position, is comparatively exempt from the direct influence of 
tributary waters. 
Both in September and in October the temperature of all these 
bodies of water is lower at Ardlui than at Luss, but the contrast is 
much greater in the colder than in the hotter month. 
