Birge—Heat Budgets of American and European Lakes. 203 
which is lower than in l any other year except one. The changes 
made in the figures for 1894 and 1895 alter these from i the small¬ 
est budgets to the largest. The excess is due to the exception¬ 
ally low winter temperature for 1895, which is nearly 1.0° 
(18,500 cal.) ibelow the mean of the other five years recorded. 
I have not included in the record the figures given in TIalbfass , 
paper of 1905 I for the years 1887 and 1889, since these should 
probably be increased like the numbers for later years. If the 
budget ’98-’99 is omitted, the mean of the total number record¬ 
ed will be increased 1500 cal. It will probably not be far wrong 
if (the mean for Como is reckoned at 32,000 cal.—33,000 cal., and, 
therefore, very close to that recorded for lago di Bolsena. 
The exceptionally small budget ’98-’99 (depends on the com¬ 
bination of an unusually low summer temperature, and an un¬ 
usually high (winter temperature. The difference as measured 
in degrees is not very great, but since the mean depth of the 
lake is nearly 200 meters, the difference in the heat budget is 
very large. 
No. 13. Lake Geneva.—-For (this lake, north of the Alps, we 
have a considerable number of budgets as we have for lake Como 
south of'the Alps. The maximum budget is above that of Como; 
the minimum is higher than Como’s minimum, and the average 
is also considerably greater. These lakes lie in substantially the 
same latitude. Lake Geneva is the larger which would tend 
to increase its (budget, but it is also the shallower, which, if this 
fact has any influence in lakes so deep, would be in the opposite 
direction. The main cause for the greater heat budget of lake 
Geneva seems to lie in the colder winter, wdiich reduces the tem¬ 
perature to a point where the heat can be more rapidly absorbed 
than is possible in Como. 
It may be noted that the minimum budget for lake Geneva is 
less than half the maximum, a ratio not very different from that 
found in Como. 
During the summer the Rhone carries an enormous volume of 
cool water into lake Geneva and an equally large volume of 
warm water is drawn off from its surface. It does not appear, 
however, that this fact operates to reduce the annual heat bud¬ 
get of the lake. The annual heat budget of lake Geneva is 
higher than that of any other lake in the table except loch Ness 
and Mjosen. It is substantially the same as that for Mjosen 
if the single exceptionally high budget of Mjosen is omitted. 
