1880 .] 
69 
[Nichols. 
The maximum temperature at a distance of from 0 to 30 meters 
from the surface was reached in July or August, from 30 to 140 
meters the maximum was reached in October, and from 120 to 
200 the maximum was not reached until December. 
Take also the observations of Fischer-Ooster and C. Brunner on 
the Lake of Thun. At depths of from 10 to 60 feet the maxi- 
mum of temperature was reached in September, at 80 feet in 
October, from 120 to 250 feet in November; at 350 feet the maxi- 
mum was reached in August, which seems to be exceptional. 
It would also seem that, in the case of some ponds which do 
not freeze in winter, the maximum of temperature is not reached 
until spring. Thus in the Lake of Thun the minimum seemed to 
be reached in February at depths from 10 to 80 feet ; in March 
from 120 feet to the bottom, but unfortunately the February was 
that of 1849 while the March was that of 1848. These observa- 
tions, although very scanty, would seem to indicate something of 
the nature of the waves of heat noted in the observations which 
have been made on ground temperatures. 
One fact of general belief whfch seems, at first sight, to be con- 
firmed by the researches of Forel on the Lake of Morat and by 
my own observations on Fresh Pond, is that after a coating of 
ice has once formed there is no further cooling of the water, the 
cold effecting simply a thickening of the ice-coating. In fact it 
would seem that the water tends to warm up, or that at any rate, 
the temperature tends to equalize itself. Thus in 1879, the mean 
of the temperature at the three different depths in Fresh Pond 
was on January 2, 0°.8 ; on January 14, 1°.2, on January 22, 1°.6. 
Meanwhile the pond fell 0.2 foot, which is equivalent to the loss of 
about 8,000,000 gallons, but during the same time there were act- 
ually pumped about 50,000,000 gallons. Thus the pond received 
some 42,000,000 of gallons between January 2 and January 22. 
The bulk of this must have come in as ground-water with a tem- 
perature much above that of the pond, but, whether the observed 
rise of temperature is more or less than would be accomplished 
by this entrance of ground-water, the data for determining are 
insufficient. 1 
x It should be said that in the case of Fresh Pond a large amount of ice is removed 
as soon as itds thick enough to be of commercial value, so that there is generally more 
or less open water. 
