20.2 millimetres. The highest observation was 30.14 inches (765.7
millimetres) on December 9, and the lowest 28.02 inches (711.7
millimetres) on May 24, 1911; difference, 54 millimetres.

Air Temperature and Thermometers.

As has already been stated, minimum thermometers and mercury sling
thermometers were wanting. For the first six months only toluene sling
thermometers were used. Sling thermometers are short, narrow glass
thermometers, with a strong loop at the top; before being read they
are briskly swung round at the end of a string about half a yard long,
or in a special apparatus for the purpose. The swinging brings the
thermometer in contact with a great volume of air, and it therefore
gives the real temperature of the air more readily than if it were
hanging quietly in the screen.

From October 1 a mercury thermometer was also placed in the screen,
though only one divided to whole degrees; those divided to fifths
of a degree would, of course, have given a surer reading. But it is
evident, nevertheless, that the toluene thermometers used are correct
to less than half a degree (Centigrade), and even this difference
may no doubt be explained by one thermometer being slung while the
other was fixed. The observations are, therefore, given without any
corrections. Only at the end of December was exclusive use made of
mercury thermometers. The maximum thermometers taken proved of so
little use that they were soon discarded; the observations have not
been included here.

It was due to a misunderstanding that mercury thermometers were
not also used in the first half-year, during those periods when