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Proceedings of Royal Society of Edinburgh. [sess. 
average temperature for the 24 hours is lower than the mean of 
the summit and Fort-William. As might he expected, the differ- 
ences rise to a maximum about mid-day, and fall towards evening. 
That with the summit occurred at 2 p.m., and that with the base 
at 12 noon. 
As formerly mentioned, the slope of the hill entirely obstructs 
the eastern horizon, thus shading the intermediate station from 
solar action in the morning. This, coupled with the fact that the 
summit is open to such action, probably explains the relative 
closeness of the intermediate and summit temperatures in the 
early part of the day. 
Table IV., at the end of this paper, gives the hour to hour 
differences in accessible form. As the maximum and minimum 
thermometers were read four times a day, it is possible, where no 
actual observation was made, to estimate the temperature at any 
given hour of the day with some approximation to accuracy. Such 
interpolations are marked with brackets. 
On 14 days out of the 23, the difference from the summit was 
relatively small in the morning and larger at night ; on 6 it was 
large in the morning and smaller at night; on 2 it was nearly 
the same ; and on 1, the fifth, it was very small in both cases. 
There was one occasion, on the morning of the 6th, when the 
temperature at the top of the mountain was higher than that at the 
middle ; but unfortunately, owing to an accident, no observation 
was taken at the intermediate station before noon. According to 
the maximum thermometer, however, it could not have been more 
than 48°'l, and was probably much less, while the readings at the 
summit for the hours of 9 and 10 were 46°”0 and 48°*7, dropping 
within the next hour to 43° "2. 
The temperature at the middle station was closest to that of the 
summit — (1) At 9 h. on the 1st of the month, when it was 
1°‘4 higher. The wind was hf.E., light. There was sunshine, and 
the station was between two fog-systems — that is, fog above and 
below, with a clear space between. 
(2) At 9 h. on the 2nd it was 2°*9 higher ; wind hf.E., light, and 
mist enveloping station, with occasional breaks. 
(3) At 9 h. on the 5tli it was 2°’8 higher; wind id., moderate 
in force, and station between fog-systems in sunshine. 
