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The Influence of High Winds on the Barometer at the Ben Nevis Observatory* 



By Alexander Buchan, LL.D. F.R.S. 



part I. 

 In Part I. the influence of high winds on the barometer is examined for all directions 

 of wind taken together ; t but in Part II. the different directions of wind are treated 

 separately. The question of the effect of wind on the readings of the barometer was 

 first examined by Sir Henry James in a paper read to the Royal Society of Edinburgh 

 on 15th March 1852.} The observations were made during the succession of gales 

 from the south-west which occurred in January and February of that year at Granton, 

 near Edinburgh, with an aneroid barometer, laid horizontally in succession on the table 

 of a room in a cottage, on the seat of an open summer-house, and on the surface of 

 the ground close to the summer-house, all at the same level. The anemometer employed 

 was of a very simple construction, being on the same principle as the instrument used 

 for weighing letters, the weight or pressure being indicated by the compression of a 

 spiral spring in a tube. A table of results is added, giving the depression of the baro- 

 meter in decimals of an inch for different velocities of wind from 14 to 40 miles per 

 hour. At 14 miles the barometric depression was 0*010 inch, and it increased gradually 

 to a depression of 0'045 inch at 40 miles per hour. Unfortunately, the number of 

 observations on which the depression for each wind velocity has been deduced are not 

 given, and the observations in the cottage and those at the open summer-house are 

 combined into one result. 



It may be assumed that the results arrived at indicate too large barometric depres- 

 sions for the different wind velocities as barometers are usually observed, namely, in 

 houses. The depression on the lee side of any obstruction in the wind, such as a 

 summer-house, is greater than it is in the room of a dwelling-house. 



Further, a barometer laid on the ground during strong winds will, if the wind brush 

 briskly over the key-hole of the instrument, indicate a less pressure than that of the 

 air. Since, however, in such a position, the wind will only at a few points have access 

 to the connecting opening between the aneroid and the free atmosphere, it may be 

 assumed that the instrument will, in the great majority of cases, show a lower reading 

 than that of the free atmosphere. 



For these reasons, the barometric depressions are probably too large. 



Since 1852, meteorologists have taken little, if any, action on the results of Sir 

 Henry James's inquiry in discussions on barometric readings and wind velocities ; and 



* See Journal of Scottish Meteorological Society, vol. ix. p. 132. 



t See Proc. Roy. Soc. Edin., vol. xviii. pp. 88-94, which details the results of the first six months ending with 

 • January 1891. 



X Trans. Roy. Soc. Edin., vol. xx. p. 377. 



