92 REPORT—1885. 
summer, and autumn, is above the daily mean for fifteen hours, from 10 a.m. 
to midnight, and below it for nine hours, from 1to94.m. In June, when 
the sun’s heat is most powerful, the afternoon minimum is the least 
pronounced, and the diurnal curve of pressure tends towards a single 
maximum and minimum, similar to what occurs in the same months over 
the open sea in the higher latitudes. Except in mid-winter these seasonal 
peculiarities of the pressure are seen in the results of each month’s obser- 
vations, and the regularity in the changes from month to month, in the 
times of occurrence of the four phases of the pressure, is very striking. 
The sunshine-recorder shows 464 hours of sunshine for the twelve 
months, which is about 11 per cent. of the possible sunshine. As regards 
the partition of the sunshine through the hours of the day, the most note- 
worthy circumstance is that during spring, summer, and autumn the 
amount is very considerably greater before noon than after it. As com- 
pared with the afternoon, the sunshine of the forenoon is 43 per cent. 
greater in spring, 50 in summer, and 33 in autumn, whereas in winter the 
amounts are nearly equal. During summer the maximum sunshine occurs 
from 6 to 94.m. This diminution in sunshine later in the day is no doubt 
caused by the ascending aerial currents which rise from the heated sides 
of the mountain during the warm hours of the day, and the condensation ” 
of the aqueous vapour into cloud which is the consequence. 
Very heavy rainfalls are of frequent occurreace on Ben Nevis. Of 
single hours the largest was 1-302 inch, from noon to 1 p.m. of December 
10, 1884. The largest daily fall was 4-264 inches, on December 10, 
1884, a fall all but equalled by that of October 25, which was 4°231 
inches. A fall of at least one inch occurs, on the average, one day in 
seven. Combining all the rainfall observations made since June, 1881, 
the following are the averages; those from July to September being for 
four years, June and October for three years, and November to May 
one year only. 
inches inches inches 
January . : ait doen SMa: F : . 837 | September . - 944 
February . , . 16:94 | June. : . . 880 | October : . 11:08 
March . : . 12°89 | July. : : . 10°70 | November . . 19°30 
April : : . 4:85 | Angust . 5 . 11:24 | December . . 25°20 
Year, 146°14 inches. 
There can be little doubt that the Ben Nevis Observatory has the 
largest rainfall of any place in Scotland at which a rain-gauge has hitherto 
been observed. 
The observations at Fort William by Mr. Livingston, consisting of 
eye observations six times a day, and continuous records of the atmo- 
spheric pressure and temperature by a barograph and thermograph, 
have been regularly carried on during the year. It is not possible to 
over-estimate the value of these sea-level observations at Fort William, in 
their relations to the observations made on the top of Ben Nevis, it being 
from these relations that the Ben Nevis observations have their supreme 
importance in discussing the great problem of the weather changes of 
North-western Europe. This inquiry is now being carried on under the 
superintendence of the Directors of the Observatory. 
