Meteorological Observations on Ben Neris.-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 was 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 as well as by day have been made uninterruptedly by Mr. Omond and his assistants during the year at the Ben Nevis Observatory; and 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 four years. The Directors of the Observatories tender their cordial thanks to Messrs. C. M. Stewart, B.Sc., A. D. Russell, and C. T. R. Wilson for valuable assistance rendered as volunteer observers during the summer months for about six weeks each, thus giving greater relief to the members of the regular observing staff. For the year 1894, Table I. shows the monthly mean and extreme pressures and temperatures, hours of sunshine, amounts of rainfall, number of fair days and of days when the amount exceeded one inch, the number of hours of bright sunshine; and this year for the first time the mean rainband (scale 0-8) at both Observatories, and the mean hourly velocity of the wind in miles at the top of the mountain. The mean barometric pressures at the Low Level Observatory are reduced to 32° and sea level, while those at the top of the Ben are reduced to 32° only. TABLE I. 1894 Jan. Feb. March April May June July Aug. Sept. Oct. Nov. Dec. Year Mean Pressure in Inches. Ben Nevis Ob- 24.980 25.086-25-192 25-286-25-357 25-450) 25-369 25-339 25-665 25-357) 25-181 25-232-25-291 servatory Fort William 29-595 29-697-29-764 24844 29-951 29-96029-820 29-823 30-232-29-31539-716-29-828-29-845 ., 4·615, 4611, 4572 4:558, 4594, 4510, 4451, 4481 4.567 4558 4-535 4-596 4-554 Ben Nevis Ob- 217 servatory Mean Temperatures. 240 28-2, 31-1 291 3-2 43-339-237-3 327 31-3 27-6 32-0 Fort William 39.3 40-3 42.3 48:4 46.9 54.8 58.9 55.2 51.0 45.6 46.7 41.1 47.6 147 17:3 17.8 166 156 160 13-7 12.9 15:4 13-5, 15-6 Extremes of Temperature, Maxima. 63.5 62.9 53.9 55.1 55.5 426 41-0 63.5 Ben Nevis Ob- 28.4 36.2 41.2 40-8. 48.1 TABLE I.-continued. Feb. March April May June July Aug. Sept. Oct. Nov. Dec. Year Rainfall in Inches. 11.79 13.62 Ben Nevis Ob- 15-96 33-55 14-581 3.50 6.66 8:33 11:35 1770 1.32 4:68 17:40 14-93 149-96 9-36 1.37 3.78 3.13 5.70 7.72 0.24 At Fort William the mean temperature of the whole year was 47°·6, or 0°.8 greater than the mean of previous years, being the excess above the mean at western stations in Scotland from Ayrshire to Ross-shire. The mean temperature at the top of Ben Nevis was 32°0, or 0°.9 above the mean for the same years, being thus nearly the same excess as at the lower Observatory. The lowest mean monthly temperature at Fort William was 39°-3 in January, being 0°-7 above the mean; and at the top of the Ben 21°.7 in January, which is 21 under the mean. This gives an unwonted large difference of temperature between the Observatories for January, which was occasioned by a comparative absence of anticyclonic weather and the relatively low temperature accompanying at the upper station, and the singular want of sunshine, there being registered for the whole month only three hours of sunshine. On the other hand, anticyclonic weather was of frequent occurrence in September, October, and December; and accordingly in these months sunshine was large, being absolutely the highest hitherto recorded in September and October, and having been only exceeded in December. It will be also observed that during these months the difference of temperature between the two Observatories was much less than usual, owing to the higher temperature of the anticyclones at the top of the Ben. The highest monthly mean temperature at Fort William was 58°.9 in July, or 2°.2 above the mean; and at the top 43°3 in the same month, or 3°0 above the mean. The month of greatest excess above the average was November, whose mean temperature at Fort William was 46°7, or 4°.1 above the mean, while at the top it was 31°-3 or 3°.2 above the mean. This great excess of temperature was about the same in all parts of Scotland, and was occasioned by an extraordinary predominance of south-westerly wind, which exceeded any observed in November during the past forty years. The sunshine was markedly deficient, and hence temperature at the top was relatively lower than at Fort William. The following show the deviations of the monthly results from their respective means :— The maximum temperature at the top was 63°5 on June 30, and 81°5 at Fort William on July 1. The minimum temperature at the top was 0°7 on January 6, and at Fort William 20°-8 on January 6. The above minimum temperature 0°.7 is absolutely the lowest yet observed on the top of Ben Nevis. The conditions under which it occurred are seen in the following extract from the day's observations : TABLE III.-Weather accompanying Low Temperature of January 6, 1894. This low minimum temperature occurred at the same time as the lowest barometric reading of a small satellite cyclone passing over the British Islands (see Daily Weather Reports). As the centre of the disturbance advanced, temperature very rapidly fell, and thereafter rose steadily, but more slowly than it had fallen, and the easterly winds acquired a little southing. The wind was high throughout, attaining at 7 A.M. a velocity at the rate of 43 miles an hour, accompanied by constant fog and showers of snow. It is this type of weather, a temperature approaching zero, near the point of saturation, and fog drifted onward with very high wind, which is the most disagreeable and prejudicial to health of all weather encountered at this high elevation. It may also be noted that the dip in the temperature was coincident with the dip in the barometric pressure. The registrations of the sunshine recorder on the top show 810 hours out of a possible 4,470 hours, being 130 hours more than in 1893. This equals 18 per cent. of the possible sunshine. The maximum was 126 hours in September, which is higher than any previously recorded September; and the minimum 3 hours in January, being the lowest yet recorded in this month. At Fort William the number for the year was 1,160 hours, being 95 hours in excess of the previous year. As the number of hours of possible sunshine at Fort William is, owing to the surrounding hills, only 3,497 hours, the sunshine of 1894 here was 33 per cent. of the possible number. TABLE IV.-Lowest Hygrometric Observations during each Month of 1894. Of these lowest monthly humidities the lowest (9) occurred at 1 P.M. on February 14, at which hour the dew-point was -27.6° and the elastic force 0010 inch. The previous month (January) presents a striking contrast to this, the lowest humidity being no lower than 57. It is also to be noted that during the eight months from April to November the dew-point on no occasion fell to zero. At the top the percentage of cloud covering the sky was 81, being 3 less than the average of previous years. The variation during the months was great, being above 90 per cent. in January, February, and November; while, on the other hand, the minimum was 58 per cent. in September and 69 per cent. in October. At Fort William the annual mean was 72 per cent., the maximum being 84 per cent. in November, and the minimum 54 per cent. in March. The mean rainband (scale 0-8) observations at the top was 2.0 for the year, the maximum being 2.7 in February and the minimum 1.5 in September, when the weather was eminently anticyclonic. At Fort William the means were for the year 4.0, the maximum 5·3 in July, and the minimum 3.0 in January and December. The mean hourly velocity of the wind at the top was 16 miles, the monthly mean maximum being 26 miles in January, and the minimum 10 miles in June. For the five months from May to September the mean was 11 miles per hour, but for the six months from November to April the mean was 20 miles per hour. The relations here indicated among the seasons substantially hold good year by year. The rainfall for the year at the top was 149.96 inches, being 3.63 inches above the average. At Fort William the amount was 79-17 inches, which is 4.07 inches above the average. The maximum monthly rainfall at the top was 33.55 inches in February, and the minimum 1:32 inch in September. At Fort William the maximum monthly fall was 13.62 inches in February, and the minimum fall 0-24 inch in September. The above are the smallest monthly amounts yet recorded at either of the Observatories, and the maxima are higher than any hitherto recorded for February. These two months were a strong contrast to each other. In February, cyclone succeeded cyclone in swift succession to each other accompanied with heavy and destructive gales, deluges of rain, and heavy snowfalls; whereas September was for much the greater part of the month under the influence of anticyclones, accompanied with clear sky, dry and wellnigh rainless weather. At the top of the Ben 6.67 inches of rain fell on February 6, being, except on October 3, 1890, the greatest daily fall on the records of the Observatory. At the top the rain fell on 246 days, and at Fort William on 208 days, being respectively 14 and 30 days under their averages. The maximum number of days on which rain fell at the top and at Fort William was 27 days in January, and the minimum number 9 days at the top and 5 at Fort William in September. During the year the number of days on which an inch of rain was exceeded was 46 days on Ben Nevis and at Fort William 16 days. In February the numbers were 11 days and 3 days respectively. Auroras are reported to have been observed on the following dates : February 13, 25; March 24, 25, 30, 31; April 28; August 23, 31; September 1, 2, 27, 30; October 2, 4, 5, 26, 27, 30, 31; November 23, 24, 26; December 1. St. Elmo's Fire was seen on January 25; February 4, 9; March, 3, 5, 6, 9, 12; May 29, 30; June 18; July 7, 21; November 8, 15. The Zodiacal Light was observed on March 24, 25, 26. Thunder and lightning reported on February 3, 8; July 6, 7, 21; August 15; September 17; lightning only on January 29, February 4, 25. Almost daily during the last week of February there were strong earth-currents in the telegraph cable between the base and summit of the hill. At Fort William the mean atmospheric pressure at 32° and sea-level was 29.845 inches, and at the top 25-291 inches, the difference being thus 4.554 inches, being only very slightly above their averages. At the top the highest pressure during the year was 25.992 inches in June, and the lowest 23-742 inches in December, the difference being 2.250 inches, a rather large difference. Mr. A. J. Herbertson has made further progress in carrying on, at the two Observatories and in the south of France, the research on the hygrometry of the atmosphere referred to in last report. The work is now in an advanced stage of preparation, and the results will shortly be |