TRANSACTIONS OF SECTION A. 595 



7. On the Thermal Windrose at the Ben Nevis Observatory. 

 By Angus Rankin. 



The direction of the wind and the temperature of the air form two of the 

 meteorological elements observed and recorded hourly at the Ben Nevis Observa- 

 tory, When making observations, the directions of the wind are referred to the 

 thirty-two points of the compass ; but in computing the results, which are briefly 

 described in this paper, the directions were referred to eight points only — namely, 

 N., N.E., E., &c. All the remaining points were taken into account by annexing 

 them in the usual way to these octants. The temperature of the air was that 

 indicated by compared thermometers, protected in Stevenson screens, with their 

 bulbs at the standard height of 4 ft. above the surface of the ground or the snow. 

 In calculating the mean temperature of the eight directions of wind, the thermo- 

 meter readings were tabulated under the directions of wind observed at the same 

 liours, or under their octants, and the mean taken for each direction for the dif- 

 ferent months, for the year, and for the seasons. The observations so treated were 

 those of the three years ending May 1887 ; and the results here discussed are on 

 the mean of these years. 



These results show that the south wind has the highest yearly mean tempera- 

 ture — namely, 32°-6, and the north-east the lowest — namely, 26°'5. In each of the 

 seasons the north-east wind is the coldest, and with one exception the south is the 

 warmest, the exception being winter, when the warmest is the south-west. The 

 point having the highest mean temperature does not remain the same throughout 

 the months, but oscillates considerably. This point during the winter months is 

 south-west, but as the year advances it swings round through south to south-east, 

 which is its direction in July and September. The coldest point has not so marked 

 an oscillation. The explanation of this oscillation in the direction of the warmest 

 wind is that the south-east wind blows over land and the south-west over sea — 

 land areas being subject to greater extremes of temperature than sea areas. The 

 annual range in mean monthly temperature is greatest for south-east winds, being 

 24°-3, and least for north-west winds, being 14'''4. The difference between the 

 warmest and coldest winds varies from month to month, the greatest difference 

 being 10°-7 in March, and the least 4°-2 in April, while the mean of aU the differ- 

 ences is 6°-7. The wind having the highest mean monthly temperature is the 

 south-east, its temperature in July being 44°-0 ; and that having the lowest is the 

 north-east, its temperature in March being 18°2. The winds arranged in their 

 order of highest yearly mean temperature, with their respective temperatures, 

 are : — 



S. S.W. W. N.W. S.E. E. N. N.E. 



.32°-6 32°-5 31°-4 30°-2 27°-8 27"-6 26°-5 



the north-west and south-east being equal — a curious fact, seeing, as has already 

 been noticed, that they differ so much in annual range. Each of the directions S., 

 S.W., W., and N.W. attains its muiimum temperature in January, and each of 

 the directions N., N.E., E., and S.E. in March. AU the directions except N.E. 

 and N.W. have their maxima in July, the two exceptions occurring a month 

 later. ' 



8. On a Peculiarity of the Cyclonic Winds of Ben Nevis. By^. T. Omond. 



9. Final Beport of the Committee appointed fo co-operate with the Meteoro- 

 logical Society of the Mauritius in the publication of Daily Synoptic 

 Charts of the Indian Ocean for the year 1861. — See Reports, p. 40. 



See Proc. Roy. Soc. Edin. 1886-87. 



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