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Abstract of Paper on the Winds of Ben Nevis. By R. T. Omond and Angus RankiN:* 



Noting the direction of the wind is part of the regular routine of observations at the 

 Observatory on the summit of Ben Nevis. Owing to the frequency of frozen fogs in 

 winter, anemometers are practically useless, but the record is made complete enough 

 for many purposes by the hourly observations ; at each hour of the day and night the 

 wind, at the time of making the observation, is noted, and the number of entries of 

 each wind direction in the day, month, or year must very nearly represent the relative 

 frequency of such winds for that time. Table I. is a summary giving the number of times 

 each wind is observed in each month of the year on an average of six years (1884-89) 

 expressed in percentages ; thus in January, out of the 744 hours of the month, there are 

 120 hours or 16'1 per cent, of N. wind. For the year the most frequent wind is N., 

 next come S.W., S.E., and S., all about equal, and the least frequent is E. N. is 

 the point of greatest frequency in all months except May, when S.E. takes its place ; 

 in May 1889 there were only 15 hours in the whole month with N., N.W., or N.E. 

 winds, and during three-fourths of that month the air was moving from the S. or 

 S.E. This was, of course, an exceptional month, but in the six years there are 

 only two (1887-88) in which N. was the most frequent wind in May. The exact 

 determination of northerly winds is not very easy on Ben Nevis, owing to the shape 

 of the hill : the great cliff, 2000 feet high, that forms its northern face, breaks these 

 winds up, and makes them squally and uncertain ; some may be entered as N. that 

 should be really N.E. or N.W. If we group the percentages of N., N.E., and 

 N.W., and S., S.E., and S.W. together, we get 36 '0 for the former, and 39*4 

 for the latter, thus throwing the preponderance of frequency to the southward, 

 but only by a small percentage. In either case, taking the observations as they stand 

 or as grouped, the relative frequency is totally different from what it is at sea-level. 

 For comparison, Table II. has been drawn up giving the percentage frequency of each 

 wind for all Scotland, from observations at 55 stations for the same six years (1884-89). 

 At sea-level the most frequent wind is W. ; and S.W., W., and N.W. include nearly 

 half of the total observations — more than half if we exclude calms. This latter order 

 of winds is in strict harmony with the distribution of barometric pressure over the 

 British Isles, according to Buys Ballot's law, by which the winds blow counter-clockwise 

 round areas of low pressure, such an area lying to the north of the British Islands ; but 

 the Ben Nevis winds do not fit in with such a distribution of pressure at all. and we 

 may conclude that isobars drawn at the level of Ben Nevis (4400 feet) would lie in quite 

 different directions from those at sea-level. In other words, the distribution of average 

 barometric pressure which extends over the North Atlantic and North-Western Europe, 



* See Trans. Roy. Soc. Edin., vol. xxxvi. p. 537. 



