522 



DR BTJCHAN ON THE 







Barometer Sea Level. 



Wind. 



Rain. 



Cloud to 10. 







Fort- William. 



Direction. 



Force to 12. 



Ben Nevis. 



Fort-William. 







Ins. 







Ins. 







April 



1 



29-850 



ESE 



7 



■04 



8 



8 





2 



29-763 



ESE 



11 



•10 



10 



9 





3 



29-724 



ESE 



12 



•oo 



10 



10 





4 



29-610 



ESE & E 



12 



•20 



10 



8 





5 



29-679 



ESE 



11 



•oo 



10 



9 





6 



29-847 



E & ESE 



10 



•00 



8 



10 





12 



30-192 



E&SE 



7 



•00 



7 



8 





13 



30-079 



SSE 



7 



•00 



10 



10 



June 



1 



29-948 



SE & ESE 



8 



•00 



8 



3 





2 



29-966 



ESE 



9 



•00 



5 



3 





3 



30-047 



ESE & E 



7 



•oo 



1 



1 





17 



30-072 



ESE 



8 



•oo 



10 



10 





18 



30-162 



ESE 



9 



•oo 



10 



10 





19 



30-313 



ESE 



9 



•00 



7 



2 



It is a characteristic of these winds on the top of Ben Nevis that they are altogether 

 restricted to the directions indicated in this table, viz., E., E.S.E., S.E., and S.S.E., and 

 they occasionally attain the greatest force recorded at the Ben Nevis Observatory, viz., 

 12 on the wind scale 0-12, and they also appear to be associated rather with anti- 

 cyclonic than with cyclonic weather. But they resemble the high winds of the previous 

 paragraph, in being associated with relatively much lower temperatures at the summit of 

 the hill than at the base of the hill at Fort-William. When a strong wind is blowing 

 over a hilly country the air is continually mixed by vertical movements, and thus the 

 temperature gradient for height tends to approximate to the adiabatic rate, so long as 

 no rain falls and no cloud is formed below the level of the higher station.* The 

 adiabatic change for 4400 feet is about 24°. This value has been exceeded at several 

 hourly readings for Ben Nevis and Fort- William, the greatest observed being 28°*8 at 

 2 a.m. on 19th December 1890, but the greatest difference on the mean of any whole 

 day, as stated above, has been only 22°'2 on 18th May 1900. 



The interest attached to these high winds is greatly enhanced in view of the analogous 

 observations of the upper atmosphere revealed by the service of kites. This subject will 

 be further dealt with in a subsequent Paper. But in discussing the observations 

 obtained by kites, a serious drawback is that the barometric readings cannot be used 

 except for computing the kite's approximate elevation. The only useful barometric 

 readings for purposes of forecasting are those obtained from High Level Obser- 

 vatories, the height of whose barometers has been got by levelling ; and hence 

 the heavy loss sustained by the closing of the Ben Nevis Observatories, which 

 deprives meteorologists of the only barometric readings of practical utility made at 

 a high level in North- Western Europe. 



* Handbook of Climatology, Hann, translated by Ward, pp. 268-272. 



