aN 
WORK oF ‘‘ MAUD’’ BXPEDITION—SVERDRUP 224 
deck. The wire could be guided in any desired direction, depending 
upon the direction of the wind, by means of a special pulley mounted 
on the ice a short distance from the ship. The first pulley was fas- 
tened permanently to the ice but was lost during an ice pressure. We, 
therefore, mounted the second pulley on a sledge, which could be 
taken on board at short notice. The kites, which were most used, 
were loaned to the expedition by the United States Weather Bureau. 
They were built sturdily, but were subject to hard usage on account 
of the difficult conditions. They, therefore, had to be repaired fre- 
quently, both in winter and in summer. So little was left of the 
original kites after the three years that they had to be entered as lost. 
The most interesting result from the kite ascents is, perhaps, that 
in winter the temperature of the air practically always is lower close 
to the ice than 300 meters above the ice. The mean temperatures 
derived from 60 ascents made 
during the drift in the coldest 
months, November to March, 
are represented in Figure 4. 
The full curve represents the 
conditions during the kite as- 
cents; that is, when the aver- — jgq9 
age wind velocity at theice was 
about 11 miles per hour. The 
temperature decreases with 500 
altitude in the first 136 meters, 
but increases higher up, first 
very rapidly and then more O35 -30 -25 -20 =15°C. 
slowly. The mean tempera- Wie. 4.—Mean temperatures, November to March 
ture at the ice is —28.4° C., acl ae 
os a RO Re ete ee re Sa n calm days 
while at an altitude of 1,000 
meters it is only —20.3° C. The dashed curve represents the corre- 
sponding temperature distribution in calm weather. This last curve 
may be called normal because it is of a familiar type. Kven in this 
latitude the lowest temperatures are found close to the ground on 
clear and calm days in winter because the air is cooled from below 
by contact with the surface, which loses heat by radiation. When a 
wind arises, however, the air generally becomes mixed to a consider- 
able altitude on account of the numerous eddies which are formed 
along the ground, and a normal decrease of temperature wit altitude 
is more or less established. The characteristic feature encountered 
over the Polar Sea is evidently that this forced mixing is limited to 
a thin layer of air directly above the ice. Over this Iayer comes a 
marked inversion, forming a surface of discontinuity which prevents 
further mixing. 
2000 
m. 
