Meteorological Observations on Ben Nevis.-Report of the Committee, consisting of Lord McLAREN (Chairman), Professor A. CRUM BROWN (Secretary), Dr. JOHN MURRAY, Dr. ALEXANDER BUCHAN, Hon. RALPH ABERCROMBIE, and Professor R. COPELAND. (Drawn up by Dr. BUCHAN.) THE Committee were appointed as in former years for the purpose of co-operating with the Scottish Meteorological Society in making meteorological 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.E., A. J. Herbertson, C. 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 0.01 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 10.9 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 10.1 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 11°.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 anticyclones 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 1892 TABLE I. Jan. Feb. March April May June July Aug. Sept. Oct. Nov. Dec. Year Mean Pressure in Inches. Ben Nevis Ob-25-096| 25-140| 25-362| 25-395| 25-346 25-398] 25-471| 25-301| 25-234 25-146| 25-281 25-235| 25-284| servatory Fort William 29-717 29-755 30-034 29-995 29-894 29-922 29-969 29-772 29-744 29-707 29-849 29-862 29-852 Differences 4-621 4.615 4-672 4.600 4:548 4:524 4:498 4:471 4510 4561 4.568 4627 4568| observatories. The highest monthly mean temperature at the top was 40°.7 in July, and 55°-5 at Fort William in the same month, these being respectively 0.6 above and 1°.8 under the several averages. The maximum temperature at the top was 59°1 on July 29, and 75°5 at Fort William on June 6. The minimum temperature at the top was 3°.5 on March 27 from the hourly eye-observations, and 2°.7 from the minimum thermometer. This is absolutely the lowest temperature that has occurred since the opening of the observatory in 1883, and it was observed at 6 A.M. At Fort William the minimum temperature for 1892 was 13°3 on February 19 The registrations of the sunshine-recorder show 802 hours out of a possible 4,470 hours, being 106 fewer than during the previous year. The maximum was 130 hours in July, being the highest for July hitherto recorded, and the minimum, 12, in January. At Fort William the number for the year was 1,179 hours, or 377 in excess of the number registered on the top; a difference above the average. The greatest number was 178 hours in April, and the least 19 hours in December. Since, at the top of Ben Nevis, the horizon is virtually clear all round, the total possible hours of sunshine agree with the theoretic number for the latitude. But at Fort William, owing to the surrounding hills, the theoretic number differs widely from the actual number possible to be observed. During the last three years Mr. Omond has observed the actual intervals between sunrise and sunset at the lower station with the following result: TABLE II.-Theoretical Number of Hours of Sunshine. : Thus the summit station has 984 hours more possible sunshine than the low level while 34 per cent. of the possible sunshine was registered by the sunshine-recorder at Fort William, 18 per cent. was registered at the top of Ben Nevis, or about half the per cent. recorded near sea-level at Fort William. Dry Bulb. TABLE III.—Hygrometric Readings for each Month. Jan. Feb. Mar. April May June July Aug. Sept. Oct. Nov. Dec. Wet Bulb Dew-point Elastic Force Relative Humidity 12.1 6.9 14:3 17.3 21.3 25-0 36.5 31.0 31.6 23-7 29-0 33.9 25.1 26:0 16-9 4.5 11-8-27.8 0-073 | 0·010 47 30 50 28 33 Saturation = 100 Of these relative humidities the lowest, 7, occurred at 3 P.M. of December 24, and from 3 A.M. of the 24th to 10 A.M. of the 28th of that month the humidity did not exceed 20. At the time of lowest humidity the calculated dew-point fell to -27°.8. Each month, from December to May, the dew-point fell below the zero of Fahrenheit's scale. The rainfall for the year was 150-90 inches, being 27.12 inches less than in 1891, and 47:44 inches less than in 1890. At Fort William the amount was 73.28 inches, or less than half of what fell at the top of the Ben. These amounts are in each case very near their averages. Mr. Omond has com |