430 



NA TURE 



[August 31, 1893 



" An exhaustive examination of the 'Winds of Ben. Nevis ' 

 has been made by Messrs. Omond and Rankin, and the results 

 published in the ' Transactions of the Royal Society of Edin- 

 burgh.' It is shown that while the sea-level winds in this part 

 of Scotland are, with respect to the distribution of pressure, in 

 accordance with Buys Ballot's 'Law of the Winds,' the Ben 

 Nevis winds do not fit in with such a distribution of pressure, but, 

 on the contrary, point to a widely different distribution of pressure 

 at the height of the observatory — 4407 feet above the sea — as 

 compared with the distribution at sea-level. In large storms, 

 with a deep barometric depression in the centre, the Ben Nevis 

 winds are practically the same as at lower levels ; but with 

 smaller storms, whose central depression is much less, great 

 differences are presented. In such 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 the opposite direction, suggesting an 

 upper outflow from the cyclone towards the anticyclone ad- 

 joining it at the time. It is further remarkable that this out- 

 flowing seldom or never occurs when the centre of the storm is 

 to the south or west, but only when it lies to the north or east, 

 or in the region where at the time the weather is coldest and 

 driest. If the wind on the hill-top is not at a right angle or a 



movements. It may be added that, with respect to therelatio 

 of the winds to the low-level isobars, Ben Nevis Observatory 

 more pronouncedly a high-level observatory in winter than i 

 summer, or, more generally, in cold than in warm weather." 

 The influence of high winds upon barometric pressure has als 

 been investigated. A comparison of readings of the baromeli 

 and anemometer at both the high and low level observatorii 

 shows that "in calm weather the two reduced barometers ai 

 practically the same, but with every increase of wind whic 

 sweeps past the higher observatory the depression of tl 

 barometer inside steadily augments. It is not till a velocity 1 

 more than 20 miles an hour is reached that the depressic 

 amounts to one-hundrtdih of an inch. At 57 miles it is oo; 

 inch, at 77 miles 0'I04 inch, and at 99 miles o'ljO inch, j 

 forecasting weather it will be necessary to keep this effect 

 high winds on the barometer constantly in mind, with the vie 

 of arriving at a better approximation to the geographical di 

 tribution of pressure at the time the forecasts are being framed 



Kelalion oj Differences of Temperalure to those of Pressut 



A discussion of the differences between simultaneous readini 



of pressure and temperature at the two observatories shows ih 



"during the period of occurrence of an anti-cyclone, when tl 



HiHHf 



Fig. 3. — Observatory covered with Fog Crystals — an Observer at Work. 



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 prostrate trees lie 

 practically in one direction over wide regions, show impressively 

 how much observation has yet to contribute before a satisfactory 

 theory, or even a merely correct description of storms can be 

 propounded. 



"The winds at Santis, Puy de Dome, and other high-level 

 European observatories, which may all be practically regarded 

 as situated in ami-cyclonic 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, constituting it a 

 class by itself, the differential ing cause being the circuujslance 

 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 and atmospheric 



NO. 1244, VOL, 48] 



temperature at the top of the mountain, with reference lO'Al 

 at Fort William, is highest, the pres.sure at the top, reduced 

 sea-level, is 0^047 inch higher than at Fort William ; and, > 

 the other hand, when the temperalure at the top is very grea; 

 lower than the average as compared with that at Fort Williai 

 the pressure at the top, reduced to sea-level, is 0'029 inch low 

 than that at Fort William. There is, therefore, a mean diff^ 

 ence of o'o76 inch of pressure for these two distinct types 

 weather. The broad result is this, and it is clear and explic 

 that when the higher observatory has the higher temperatur 

 and also when the differences of temperature are small, thent 

 reduced pressure at the top of the mountain is the greater oft 

 two; but when the differences of temperalure are large, th 

 the reduced pressure at the topis the lesser of the two. . . . T 

 result, which is altogether unexpected, raises questions of I 

 greatest importance, affecting the theory of storms, the effect 

 vertical movements of great masses of air on the baromen 

 pressure which accompanies cyclones and anti-cyclones, and t 

 necessity there is for some accurate knowledge of the absoli 

 amounts of aqueous vapour at different heighis in the atn 

 sphere under different weather conditions, and how this knc 



