280 REPORT— 1893. 



Meteorological Observations on Ben Kevis. — Report of the Coon- 

 riiittee, consisting of Lord McLaren ( Chairman), Professor A. 

 Crum Brown (Secretary), Dr. John Murray, Dr. Alexander 

 BucHAN, Hon. Ralph Abercrombie, and Professor E. Copeland. 

 [Draivn tip by Dr. Buchan.) 



The Committee were appointed as in former years for the purpose of 

 co-operating with the Scottish Meteorological Society in making meteoro- 

 logical observations on Ben Nevis. 



The hourly eye-observations by night and by day have been made 

 during the past year at the Ben Nevis Observatory without a single 

 interruption by Mr. Omond and his assistants ; also the continuous 

 registrations and other observations have been carried on at the Low Level 

 Observatory at Fort William with the same fulness of detail as during 

 the previous two years. 



The Directors of the observatories tender their cordial thanks to 

 Messrs. R. C. Mossman, F.R.S.B., A. J. Herbertson, 0. Stewart, B.Sc, 

 J. I. Craig, and A. Shand for valuable assistance rendered as volunteer 

 observers during the winter and summer for periods varying from four 

 to ten weeks, thus affording much needed relief to the members of the 

 regular observing staff. 



For the year 1892 Table I. shows the monthly mean and extreme 

 pressures, temperatures, hours of sunshine, amounts of rainfall, number 

 of fair days or days of less than 01 inch of rain, at the observatories, 

 the mean pressures at the top of the Ben being reduced to 32° only, 

 while those at Fort William are reduced to 32° and sea-level (see 

 Table I.). 



The mean temperature of the whole year at Fort William was 45°'3, 

 being 1°'9 less than the mean of previous years, being nearly the deficiency 

 for 1892 of a large part of Scotland to the north and east of Fort 

 William. The mean temperature at the top of Ben Nevis was 29°"7, 

 which is 1°1 under the mean. Thus the mean temperature at the top, 

 as compared with the foot of the mountain, was 0°"8 relatively warmer, 

 and this relatively higher temperature was maintained at all strictly 

 island and sea-coast situations from Monach in the Outer Hebrides to 

 Corsewall Point, Wigtownshire, just as occurred in 1891. The difference 

 was occasioned chiefly by the temperatures of the spring months and 

 December. 



The lowest mean monthly temperature at Fort William was 35°'3 in 

 December, being 4°"6 under the mean ; but at the top of the Ben 20°'3 

 in March, being 2°'3 under the mean. At the top the mean for December 

 was 24°'0, being only 0°"7 under the average ; whilst, as stated above, 

 the mean of Fort William was 4°"6 under the average. The difference of 

 the means of the two observatories was only ll°-3, instead of the normal 

 15°'2. This remarkably higher relative temperature of the top in 

 December was altogether due to the prevalence of well-marked anti- 

 cyclones during the time, when the temperature at the top was frequently 

 much higher than at Fort William. It was during these periods, when 

 extraordinary dryness of the air also prevails, that Mr. Herbertson 

 succeeded in obtaining the most valuable of the hygrometric observations 

 in connection with the large inquiry he is now conducting at the two 



