1040 REPORT OF COMMISSIONER OF FISH AND FISHERIES [4] 
weather had set in. Later in the autumn a thermometer was sent to 
the superintendent (one of the owners of the lake), who was requested to 
observe here and there in the course of the winter the temperature of 
the water at the bottom. The winter cold, which set in early in Novem- 
ber, before he had received a thermometer, was unusually severe up to the 
end of March, so that a layer of ice a foot thick was formed over the 
lake. In the beginning of April he reported that the temperature at the 
bottom, in a depth of 23 feet, was 10° R. (54.5° F’.), though the water was 
not yet free from ice. They betieved in Stavanger that he had read 
incorrectly, but repeated examinations gave the same result. When 
Gundersen visited the lake in May, to place new collectors and examine 
the old, he found the temperature of the water 14° R. (63.5° F.), at a 
depth of 33 feet. This seemed incomprehensible to the members of 
the company, and gave occasion for many guesses as to the cause which 
coyld possibly produce the high temperature of the bottom water. The 
flowing out of warm springs in the bottom of the lake was regarded by 
some as the most probable, while others attributed it to the heat de- 
veloped by the putrefaction (fermentation) of the masses of contervee. 
When they asked my opinion as to the explanation of this curious 
circumstance, I reserved it until, by a longer stay in the place, I had 
carefully examined the conditions which probably in connection with 
one another would give a better basis of explanation for the unques- 
tionable fact than those propounded above, both of which seemed to me 
inadmissible. Last summer and fall I remained twice for a long time 
at the lake, and after my return to Christiania, I stated at one of the 
meetings of the scientific society my explanation of the causes of the 
exceptionally high temperature of this basin, both in summer and win- 
ter, a temperature which makes this lake, scarcely two hectares in area, 
with an average depth of 26 feet, a tropical water oasis in our cold north, 
and thereby a forcing-house for oysters. I hope that my explanation 
will be satisfactory to the scientific public since it has been sanctioned 
by our well-known hydrologist, Protessor Mohn. 
I suppose the causes to be the following: 
1. Its situation, protected from all cold winds ; because only the milder 
westerly winds coming from the sea can affect the surface of the lake, 
and that but slightly. Through the valley, which leads up to the lake 
from the north, from which originates the brook spoken of, a portion of 
Oyster Lake, it is true, can be affected by cold northerly wind, but the 
cooling effect of this wind, taken altogether, is comparatively slight, 
and when the lake becomes ice-bound and afterwards snow-covered, the 
cooling off will be reduced to a minimum. 
2. The black color of the bottom is, according to my opinion, compared 
with the remaining reasons, the chief cause of the high temperature of 
the lake water; to this also the dark color of the mountain sides men- 
tioned contributes in no small degree, in that, being illumined by the 
sun, they radiate a heat, which in the stratum of air saturated with 
