210 Wisconsin Academy of Sciences, Arts, and Letters, 
of the lake and 34 km. from the south end.* * The 400 m. contour 
extends within about 16 km. (less than one-fifth of the total 
length of the lake) of the south end of the lake. The observa¬ 
tions of 1901 did not extend below 400 m. If they were made 
at the south end of the deep water the apparently high mean 
temperature may be due in part to a temperature seiche and in 
part to transport of warm water from the very large north part 
of the lake and its accumulation in the south part. If the read¬ 
ings were taken near Helgoen the latter cause must have pre¬ 
dominated. This was probably the chief factor in any ease, 
since the lake has a form somewhat resembling a funnel with the 
broad part toward the north and with a narrow extension toward 
the south. This form would make it easy for a north wind to 
force large masses of the warm water into the south end of the 
lake. In any case, the high temperature of the surface water 
shows that the budget for 1901 was unusually large. 
In 1901 the temperature taken through the ice on Apl. 17 
(3.17°) was lower than that taken on Mch. 9 (3.27°). In the 
latter case the readings were taken only to a depth of 320 m. and 
probably in shallower water than the April series, which ex¬ 
tends to 420 m. Very likely the mean of 3.22° would fairly 
represent the winter temperature. The water in April was 
colder at all depths than in March and of course there was no op¬ 
portunity for the water to cool under the ice if the lake was com¬ 
pletely frozen. 
The readings of the other years for Mjosen are wholly 
reasonable: but it should be noted that the observations taken 
on Sept. 14, 1899 extend only to 200 m. and must be conjectur- 
ally supplied for the deeper water. 
There are no other series from any lake included in Table A 
which give clearly incorrect indications regarding the heat bud¬ 
get. Mjosen is a lake in which such errors would be more likely 
to occur than in any other lake included in the list. The shape 
of the lake in general, the situation of the island, the eccentric 
position of the deep water, the great length of the relatively 
shallow north arm, all combine to make it anything but a lake 
of simple form in which a single series of temperature observa¬ 
tions taken at the center may be fairly expected to indicate the 
mean temperature of the lake. (See map, Huitfeld-Kaas ? 05.) 
* The measurements are taken from the small map in Huitfeld-Kaas 
* 05 . 
