494 DR BUCHAN ON THE 



The striking features of the table are, that the highest velocities, or the velocities 

 exceeding 75 miles an hour, have been absolutely restricted to the points of the 

 compass from S.E. by S. fco E. by S. ; and that from E.N.E., E., W., W.N.W., N. W., and 

 N.N.W., no observations of the wind were recorded during the ten months exceeding 

 30 miles an hour. 



These differences are due to the physical surroundings of the Observatory. Of 

 all directions, the horizon is most open to S.E. and E.S.E.,and accordingly the heaviest 

 storms of wind have occurred only when the wind was in these directions. The great 

 cliff, immediately to the north of the Observatory, about 1800 feet high, has an all- 

 important effect in lowering the strength of all winds that blow on its face. The 

 N. wind, which strikes it most perpendicularly, has risen to a velocity of 60 miles 

 an hour ; but none of the other winds that blow against it have exceeded 40 miles 

 an hour. The difference is seen most markedly as regards E. winds and E. by S.. 

 winds. The highest yet recorded by E. winds has been 30 miles an hour ; but from 

 the adjoining point of the compass, E. by S., the very highest velocities have been 

 reached, which the observers estimate at 170 miles an hour. The differences are due 

 to the position of the cliff with reference to these two wind directions. 



It may be remarked, with regard to these high wind velocities, that they are 

 accompanied with violent pumping of the barometer. On such occasions the observers 

 set the barometer, not to the lowest points to which the mercury is seen to fall, but 

 to the point to which it is observed to rise and remain stationary for a brief interval. 

 The object aimed at is to eliminate, so far as possible, the effects of pumping from the 

 recorded observations. 



Equally conspicuous is the influence of the cliff seen in the different depressions of 

 the barometer for different directions of winds blowing with the same force at the 

 Observatory. This depression is very small with wind from the half of the compass, 

 from S.E. by W. to N.W., when the wind does not exceed 30 miles an hour. At a 

 velocity of 30 miles an hour the mean barometric depression from S. to W.N.W. is only 

 0*005 inch; whereas with winds at the same velocity from N.N.W. to E. the mean 

 depression is 0*039 inch, or nearly eight times greater. The most striking comparison 

 is afforded by N. and S. winds respectively. Thus — 



Miles per Hour. 



Depression, N. Winds. 



Depression, S. Winds. 







Inch. 



Inch. 



12 





0-020 



o-ooo 



21 





0-028 



0-003 



30 





0034 



0-005 



39 





0-052 



0-012 



49 





0-066 



0-022 



60 





0-084 



0-044 



During the prevalence of northerly winds, observations at the top of the mountain 

 indicate a much lower speed than that which, from the drift of the clouds, is seen to be 

 reached at a comparatively small height above the top of the Ben. It is probable that 



