116 DR MILLER ON THE METEOROLOGY OF 



night, and in wet weather, it is placed under a capacious shed, 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 Stations. — 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,f 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 Sea 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 

 therm ometrical 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 indehted for several interesting facts to an 

 elaborate paper " On the Physical Geography of Hindostan," by Dr Buist, LL.D., Vhich appeared 

 in the last (April) number of the Edinburgh New Philosophical Journal. 



f An extremely indurated Green slate and Porphyritic slate. 



