46 



REPORT — 1900. 



This table shows for 1899 the mean monthly and extreme pressure and 

 temperature, amounts of rainfall with the number of days of rain and the 

 days on which the amount equalled or exceeded one inch ; the hours of 

 •sunshine, the mean percentage of cloud, the mean velocity of the wind in 

 miles per hour at the top of the mountain, and the mean rainband at both 

 observatories. The mean barometric pressures at Fort William are 

 reduced to 32^ and sea level, but those at the Ben Nevis Observatory 

 only to 32°. 



At Fort William the mean atmosj^heric pressure for the year was 

 29-871 inches, being 0'027 inch greater than the mean of the forty years 

 ending 1895. The mean at the top was 25-321 inches, being 0-025 inch 

 above the average of the observation since the opening of the Observatory 

 in 1883. The difference for the two observatoi'ies was thus 4-550 inches, 

 lieing all but identical with the difference of previous years. At the top 

 of the mountain the absolutely highest pressure for the year was 26-058 

 inches, and at Fort William 30-728 inches, both readings occurring on 

 November 17. 



The differences from the mean monthly barometric pressure much 

 exceeded the averages in June, July, and August, the excess for the 

 three months for Fort William being 0-172 inch, and for Ben Nevis 

 0-160 inch. On the other hand, for January and April the deficiencies 

 from the averages were 0-161 inch and 0'160 inch for Fort William, and 

 for Ben Nevis 0-164 inch and 0-165. In the summer months, when pres- 

 sure was abnormally high, the type of weather was anticyclonic, but in 

 January and April, when pressure was unusually low, the type of weather 

 was cyclonic. 



The deviations of the mean temperature of the months from their 

 respective averages are shown in Table II. : — ■ 



The highest monthly mean temperature hitherto yet observed on Ben 

 Nevis was 48°-7 for August, which was 8°-2 above the mean of previous 

 Augusts. The excess of mean temperature of the three summer months 

 was 5°-0 above the average, whereas at Fort William the mean excess 

 was only 2°-9. In the strongly marked type of anticyclonic weather 

 which then prevailed, the temperature at the top of Ben Nevis was 

 relatively very much higher than at Fort William. Hence, while the 

 normal difference of temperature in August at the top and bottom of the 

 hill is 16°-1, in August 1899 it was only ll°-9. The absolutely highest 

 temperature for the year at Fort William was 82°-0 on August 24 ; and 

 at the top of Ben Nevis 63°-5 on August 23. The absolutely lowest was 

 15°-2 at Fort William on December 28 ; and on Ben Nevis 6° -9 on 

 March 23. 



