286 Proceedings of Royal Society of Edinburgh. [sess. 
(3) At 15 h. on the 20th it was 13°“6 higher; wind, X.W., 
very light; bright sunshine ; fog 1000 feet above. 
(4) At 14 h. on the 21st it was 12° *6 higher ; wind W., very 
light ; bright sunshine ; no fog visible. 
In three of these eases there was either no fog visible, or it was 
at a considerable height ; while in one case there was merely a pass- 
ing cloud, not affecting the station itself. 
The greatest differences from Fort-William temperature were — 
(1) At 10 h. on the 11th it was 12° - 5 lower; wind calm; no fog 
at the hour, but passing clouds. 
(2) At noon on the 16tli it was 12 0, 6 lower; wind W.S.W., 
squally ; no fog visible ; passing showers. 
(3) At 15 h. on the 19th it was 1 2° *2 lower; wind S.S.W., 
moderate ; fog about 100 feet above. 
(4) At 15 h. on the 23rd it was 12°*7 lower; wind X.N.W., 
gusty; small rain falling ; fog 200 feet above. 
The difference from summit temperature was also considerable. 
Those facts seem to point to the following general conclusion : — 
That when the station was enveloped in fog or between two fog 
systems, or close to the fog, the temperature approximated to that 
of the summit, and when there was no fog visible, or if it were at 
a great height, it approximated to that of the base. 
Table III. — As regards wet-bulb readings, the question of 
humidity is still so surrounded with difficulties that it is scarcely 
safe to enter upon it on such slight grounds. The air was dryest 
on the 13th of the month, the minimum humidity occurring at 
14 h. The mean results show that humidity was greatest at 9 h., 
declined to a minimum at 14 h., and rose again towards evening. 
The amount of cloud and fog was greater in the morning than in 
the evening, which is the normal state of things. 
Table IX. — This seems to be a fitting opportunity to enter more 
fully into a description of the fog. The height of its lower or 
upper' surface was estimated by the help of well-known marks, 
the principal of which was the elevation of the station itself — 
2190 feet. In no case would the error exceed 100 feet, and any 
height near that of the station may be assumed to be fairly 
accurate. 
