For determining the relative humidity of the air the expedition
had two of Russeltvedt's torsion hygrometers. This instrument has
been accurately described in the Meteorologische Zeitschrift, 1908,
p. 396. It has the advantage that there are no axles or sockets to
be rusted or soiled, or filled with rime or drift-snow.

Fig. 1.

Fig. 2.

Fig. 3.

The two horsehairs (h, h') that are used, are stretched tight by a
torsion clamp (Z, Z', and L), which also carries the pointer; the
position of the pointer varies with the length of the hairs, which,
again, is dependent on the degree of humidity of the air. (See the
diagrams.) These instruments have been in use in Norway for several
years, especially at inland stations, where the winter is very cold,
and they have shown themselves superior to all others in accuracy and
durability; but there was no one on the Fram who knew anything about
them, and there is therefore a possibility that they were not always
in such good order as could be wished. On September 10, especially,
the variations are very remarkable; but on October 13 the second
instrument, No. 12, was hung out, and there can be no doubt of the
correctness of the subsequent observations.

It is seen that the relative humidity attains its maximum in winter,
in the months of July and August, with a mean of 90 per cent. The
driest air occurs in the spring month of November, with a mean of
73 per cent. The remaining months vary between 79 and 86 per cent.,