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Abstract of Paper on further Results of Mr Wragge's Ben Nevis Observations, taken 



in the year 1882. By R. C. Mossman* 



The more prominent results of Mr Wragge's work were discussed by Dr Buchan in a 

 paper on the " Meteorology of Ben Nevis," published in the Journal of the Scottish 

 Meteorological Society (vol. vii. p. 4). The humidities at the intermediate stations on 

 the hill-side have not, however, as yet been discussed. One reason for this was that, 

 until Dr Herbertson and Mr H. N. Dickson carried out their researches on hygrometry 

 at Ben Nevis Observatory, it was not known how far Glaisher's tables could be 

 regarded as reliable at high-level stations. Their experiments, however, showed that 

 for temperatures above 40°, Glaisher's factors could be used except when the air was 

 excessively dry. As Mr Wragge's observations were taken between June and October, 

 when the temperature was relatively high and the air nearly saturated, Glaisher's 

 tables have been employed to compute the humidity and vapour pressure from the dry 

 and wet bulb readings. 



The following are the heights of the stations and the hours at which observations 

 were taken by Mr Wragge or his assistants when ascending and descending Ben 

 Nevis : — 



Station. 



Height. 



Hours 



of Observation. 







feet. 



h. m. 





h. m. 





Peat Moss, 



40 



5.30 





14.30 





The Boulder, . 



840 



6.15 





13.45 





The Lake, .... 



1840 



7. 





13.0 





Brown's Well, 



2200 



7.30 





12.30 





Red Burn, 



2700 



7.55 





Noun. 





Buehan's Well, . 



3575 



8.30 





11.30 





Ben Nevis Summit, 



4406 



9.0—9.30 





10.0—10.30- 



-11.0 



Simultaneously with these observations on the mountain, similar observations were 

 taken at Fort- William, with additional ones at 5h. 0m., 15h. 0m., 18h. 0m., and 

 21h. 0m. The total number of observations made at Fort-William was 3213, and at 

 the hill stations 2601. From each of these readings the relative humidity and vapour 

 pressure were computed, and the average values tabulated for each station. The mean 

 relative humidity, as is to be expected, increases with height, the only exception being 

 at " The Boulder," 840 feet, where at the morning reading at 6h. 15m. the humidity 

 was 2 per cent, below that at Fort- William at the same hour. The relative dryness at 

 this height is probably due to the occurrence of low-lying radiation fogs. The diurnal 

 range of humidity at Fort-William is well marked, the minimum being at about 



* See Journal of Scottish Meteorological Society, vol. xi. p. 284. 



