536 



ME MOSSMAN ON MR WRAGGE'S BEN NEVIS OBSERVATIONS. 



14h. 30m., the time of highest temperature. Little can be said about the diurnal 

 curve at the hill stations except that the amplitude diminishes with height, and 

 becomes very small above 3500 feet. 



One very interesting feature was noted, viz., that whenever a warm current on the 

 mountain was suddenly superseded by a cold one, the air at Fort- William at once 

 became drier, the fall in humidity there during the nine cases observed ranging from 

 8 to 18 per cent., and most of these changes took place in half an hour. One typical 

 case may be cited, that on 3rd September 1882. In the early morning the air below 

 was all but saturated ; and when ascending the mountain, the fall of temperature, with 

 height, was found to be less than usual up to about 2700 feet. At 8h. 30m., however, 

 a cold current of air set in at 3500 feet, and the air below became suddenly dry, though 

 the atmosphere in contact with the mountain continued in a nearly saturated condition. 

 The dry air had little vertical height, for at "The Boulder," 840 feet, the humidity 

 at 13h. 45m. was 14 per cent, greater than at Fort- William, instead of the normal 

 difference of less than 1 per cent, at that hour. On that day the weather charts show 

 that a low pressure area lay over the North Sea with its centre 600 miles N.E. of Ben 

 Nevis, and an anti-cyclone in the Atlantic, central 1300 miles to the S.W. of Ben 

 Nevis. 



Both the ascending and descending series of observations show on the mean a 

 decrease of vapour pressure with height at all stations, except the Peat Moss, at 

 2.30 p.m. in June. The differences at each station from Fort- William are given in the 

 table below, along with the rate of decrease of vapour as computed from these 

 differences. It will be seen that the average rate of decrease is substantially '003 inch 

 for each 100 feet at all the stations. 



Differences of Vapour Pressure at Ben Nevis and at Six Intermediate Stations from 



Fort- Willi am in 1882. 



Stations. 



Height. I Hour. 



Peat Moss 

 Boulder . 

 The Lake 

 Brown's Well 

 Red Burn 

 Buchan's Well 



Ben Nevis 



Buchan's Well 



Red Bum 

 Brown's Well 

 The Lake 

 Boulder 

 Peat Moss 



Feet. 

 40 

 840 

 1840 

 2200 

 2700 

 3575 



4406 



3575 

 2700 

 2200 

 1840 

 840 

 40 



5-30 

 6-15 



7-0 

 7-30 

 7 '55 

 8-30 



9-0 



9-30 



10-0 



JO-30 



11 '0 



11-30 

 Noon 

 12-30 

 13-0 

 1345 

 14-30 







Difference from Fort- William. 





Decrease of Vapour Pressure for each 

 100 Feet of Ascent. 





June. 



July. 



Aug. 



Sept. j 



Oct. 



Mean. 



1 

 June. July. 



Aug. Sept. 



Oct. 



Mean. 





Inch. 



Inch. 



Inch. 1 



Inch. 1 



Inch. 



Inch. 



Inch. 



Inch. 1 Inch. 



Inch. 



Inch. 



Inch. 



-•001 



- 021 



- 012 



-•017 



- '012 



- -013 









... 





- -022 



-•044 



-•041 



-•033 



-•027 



-•033 



•0026 j 



•0052 



•0049 



•0032 



•0031 



•0039 



-•039 



-•057 



■- -051 



-•048 



- -034 



- 046 



•0021 



■0031 



•0029 



•0028 



■0019 



■0026 



- -070 



-•083 



-•085 



-069 



-•050 



- '072 



•0032 



•0038 



•0039 



■0031 



•0023 



■0032 



-•084 



-•107 



-•095 



-•089 



-•069 



-•089 



■0031 



■0040 



■0035 



■0033 



•0026 



■0033 





-•109 



--126 



- -124 



- -no 



-•084 



- -no 



•0030 



•0035 



•0035 



0030 



•0023 



•0031 





-•117 



- -143 



-•137 



- -122 



-•099 



-•123 



■0027 



0032 



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•0028 



•0023 



•0028 





-•121 



-•111 



-•131 



-•126 



-•099 



-•124 



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•0030 



0029 



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•0028 





- -115 



-•139 



- -131 



- -126 



- -100 



- -122 



•0026 



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•0029 



■0023 



•0028 





-•118 



-•143 



-•136 



-•126 



-•102 



-•125 



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0029 



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■0028 





-•115 



- -135 



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-•119 



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-■118 



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0027 



■0023 



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-•101 



-•121 



- -no 



- -105 



-•085 



- '104 



•0021 



•0034 



•0031 



•0029 



•0024 



■0029 





-•061 



- 092 



-•088 



' --076 



- -069 



-•077 



•0023 



•0034 



•0033 



•0028 



•0026 | -0029 





-•050 



-■069 



-•061 



- -066 



- -058 



-•061 



•0023 



■0031 



•0028 



•0030 



0026 



•002S 





-•050 



-•060 



- 050 



-•052 



- 042 



- 057 



•0027 



•0033 



•0027 



■0028 



•0023 



•0028 





- -oio 



- 051 



-•038 



1 - -023 



-•025 



- '030 



•0012 



•0063 



•0045 



•0027 



•0030 



•00.36 





+ •014 



017 



-•008 



i 



- -oio 



- '013 



-•007 















