116 DR MILLER ON THE METEOROLOGY OF 
night, and in wet weather, it is placed under a capacious shed, 9 feet in height, and 
open in front. Thus, it is considered that the evaporating surface is freely acted 
upon by all the circumstances concerned in promoting the vaporization of water. 
The evaporation has now been recorded with scrupulous care, day by day for 
twelve years, at this observatory; and it is believed that the results are the best 
which have yet been obtained in this country.* 
TEMPERATURE AT THE Mountain Srations.—Considerable difficulties have 
attended my endeavours to secure the monthly minimum temperature at the 
higher mountain stations. The mountain tops consist of an extremely hard and 
impenetrable rock,} so that it is impossible to fix in it a pole on which to fasten 
the box containing the thermometers. Some years ago, a party of Government 
Surveyors, engaged in triangulating from Sca Fell Pike, erected on the summit a 
cairn or pile of loose stones, having in its centre a stout pole, which projected 
about two feet above the apex of the cairn. To this pole the box containing the 
thermometers was originally attached. The box was freely pierced with circular 
holes at the sides and bottom, to permit the air to circulate freely through it. 
The horizontal thermometers were purposely disposed with a slight inclination 
downwards toward the bulb, to counteract, in some degree, the resistance offered 
to the contraction of the alcohol by the glass-pin or index; and it was not until 
the observations had been taken for a considerable time, that it was suspected, 
from the extreme degree of cold indicated, that strong currents of air passing 
through the apertures in the wooden case might cause the indices to descend to- 
wards the bulb, and so produce erroneous readings. 
It was subsequently found that the apprehended source of error was real, and 
that it must have been continuously in more or less active operation, when the 
air was in rapid motion. 
In the year 1851, I determined to make a renewed attempt to obtain correct 
thermometrical indications from self-registering instruments ; and, that I might 
not have to depend entirely on one instrument, I also stationed minimum thermo- 
meters at Sprinkling Tarn and on the Gabel, at 1900 and 2925 feet respectively 
above the sea. A rock was selected which stood about four feet above the sur- 
face, or pieces of stone and rock were collected and piled up to that height: the 
thermometer boxes were placed thereon, and built in at the top and sides with 
loose stones, so as to secure them from being displaced by the wind, and, at the 
same time, to give the air ready access to the instruments through the interstices 
of the stones and augur-holes in the cases. So placed, the instruments were also 
concealed from tourists and other casual mountain visitors. 
* In compiling the paragraph on Evaporation, I am indebted for several interesting facts to an 
elaborate paper “ On the Physical Geography of Hindostan,” by Dr Burst, LL.D., ‘which appeared 
in the last (April) number of the Edinburgh New Philosophical Journal. 
+ An extremely indurated Green slate and Porphyritic slate. 
