ON METEOROLOGICAL OBSERVATIONS ON BEN NEVIS, 143 



sncli a distribution of pressure, but that on the contrary they point to a 

 widely different distribution of pressure at the height of the observatory, 

 4,407 feet above the sea. In large storms, with a deep barometric depres- 

 sion in the centre, the Ben Nevis winds are practically the same as at lower 

 levels ; but with smaller storms great differences are presented. In these 

 cases it is remarkable that with a cyclone covering Scotland, the North 

 Sea, and Southern Norway the winds frequently blow, not in accordance 

 with the sea-level isobars, but in an entirely opposite direction, suggest- 

 ing an outflow from the cyclone towards the anticyclone near at the 

 time on the other side. It is further remarkable that this outflowing 

 seldom or never occurs when the centre of the stoi'm is to the south or 

 west, but only when it lies to the north or east. If the wind on the hill- 

 top is not at a right, or greater, angle from the sea-level wind, it is 

 usually nearly the same as it ; the supposed veering of the wind at great 

 heights required by the theory that a cyclone is a whirling column, 

 drawing the air in spirally below and pouring it out spirally above, is 

 so seldom observed as to be the exception, and not the rule. This 

 important result and the analogous observation that frequently in great 

 storms of winds prostrated trees lie practically in one direction over wide 

 regions show impressively how much observation has yet to contribute 

 before any satisfactory theory of storms can be propounded. 



The winds of other high-level European observatories, which may all 

 be regarded as situated in anticyclonic regions, have been examined, 

 and it is found that they show the closest agreement with the winds at 

 low levels in the same regions. This result separates the Ben Nevis 

 Observatory from other observatories, so as to form a class by itself, the 

 differentiating cause being the circumstance that Ben Nevis alone lies in 

 the central track of the European cyclones. This consideration emphasises 

 the value of the Ben Nevis observations in all discussions of weather. It 

 may be added that, with respect to the relation of the winds to the low- 

 level isobars, Ben Nevis Observatory is more pronouncedly a high-level 

 observatory in winter than in summer, or, more generally, in cold than 

 in warm weather. 



Mr. Rankin has communicated to the directors a paper on the results 

 of the dust-counting observations of the past year. The highest number 

 observed was 14,400 per cubic centimetre in- April last, whilst the lowest, 

 0, was observed in July, 1890, and again in March, 1891 ; and here it must 

 be noted that ea.cli observation is really the mean of ten observations taken 

 at the time. The greatest amount of dust is observed when the wind is 

 E., S.E., or S., both at sea-level and the top of the Ben ; but when the 

 winds at the top diverge most from those at sea-level then the lowest 

 dust values are obtained. We have here, broadly indicated, another con- 

 tribution to weather prognosis afforded by the dust observations, since 

 they point to quite different phases of weather. 



True fogs and wet mists exhibit marked differences. In fog there 

 is usually a considerable amount of dust ; in mist, or wet mist, usually 

 very little. It is observed when the number of dust particles noted is 

 extremely small, or even 0, thattheair is surcharged with aqueous vapour, 

 if such a condition be suppcsed possible, and that then, there being no 

 dust particles to serve as nuclei on which the vapour might condense, it 

 simply condenses en all exposed objects direct from the air. This has 

 been found to be the most wetting condition of the air, a few minutes 

 only being sufficient to give the observer a thorough soaking. Every 



