INTER-RELATIONS OF BAROMETRIC PRESSURE. 

 Class III. — Mean Daily Sunshine in Hours. 



515 







Jan. 



Feb. 



Mar. 



Apr. 



May. 



June. 



July. 



Aug. 



Sept. 



Oct. 



Nov. 



Dec. 



Year. 



Group I. — 































Temperature Differences, 































all observed 



Ben Nevis. 



0-9 



1-8 



2-5 



3-2 



4-7 



4-6 



3-0 



2-2 



2-3 



1-9 



1-3 



0-9 



2-4 



Do. do. do. 



Fort-William. 



0-9 



T9 



37 



5-0 



6-3 



6-1 



4-4 



4-0 



3-7 



2-8 



1'2 



07 



3-4 



Group III.— 































Temperature Differences, 































12 o, or less 



Ben Nevis. 



2-5 



4-5 



6-5 



7-5 



10-3 



8-9 



6-3 



5-0 



57 



5-0 



3-6 



2-1 



57 



Do. do. do. 



Fort-William. 



TO 



3-4 



5-1 



7-0 



9-0 



8-8 



5-4 



5-1 



6-6 



4-0 



2 



0-8 



4-8 



Group IV.— 































Temperature Differences. 































18° - or greater . 



Ben Nevis. 



0-4 



1-1 



2-5 



2-3 



2-7 



2-0 



1-0 



0-9 



0-6 



0-3 



0-2 



0-4 



1-2 



Do. do. do. 



Fort-William. 



1-1 



2-3 



3-8 



5-5 



5-3 



5-6 



4-6 



2-9 



3-6 



2-4 



0-9 



0-8 



3 2 



As regards sunshine, for all differences of temperature, Group L, the observations give 

 a daily mean for the year of 2*4 hours for the top and 3 '4 hours for Fort- William, rising 

 in April, May, and June, the maximum months, to a mean of 4 '2 hours for the top and 

 5*8 hours for Fort- William ; and falling in November, December, and January, the three 

 minimum months, to TO hour for the top and for Fort-William. 



Very different are the figures for Group III., where the differences of temperature 

 are 12 o, or less ; the observations give a daily mean for the year of 57 hours for the top, 

 and 4 '8 hours for Fort- William ; and for Group IV., where the differences of temperature 

 are 18°'0 or greater, in which case the mean for the year is 1"2 hour for the top and 3'2 

 hours for Fort- William, thus showing on the mountain, both on the top and at Fort- 

 William, a very much larger sunshine when there is a comparatively small difference of 

 the mean daily temperature than when the difference is large. Further, on the days 

 of small differences of temperature there occurs more sunshine at the top of the mountain 

 than at Fort- William, but, on the other hand, when the difference is large the hours of sun- 

 shine at the top are much less than at Fort -William. Thus, for the five months from March 

 to July, while the daily mean for the top is 2*1 hours, the mean for Fort- William is 5'0 hours. 



Class IV. — Mean Daily Rainfall in Decimals of an Inch. 







Jan. 



Feb. 



Mar. 



Apr. 



May. 



June. 



July. 



Aug. 



Sept. 



Oct. 



Nov. 



Dec. 



Year. 



Group I. — 































Temperature Differences, 































all observed 



Ben Nevis. 



•54 



•34 



•41 



•25 



•25 



•25 



•34 



■44 



•53 



•43 



•44 



■58 



•40 



Do. do. do. 



Fort- William. 



•23 



•16 



•16 



•10 



■11 



■12 



•15 



"21 



•25 



•24 



•22 



■30 



•19 



Group III. — 































Temperature Differences, 































12° - or less 



Ben Nevis. 



•09 



•10 



•18 



•05 



■09 



■11 



•25 



•46 



•26 



•15 



■07 



•16 



•16 



Do. do. do. 



Fort-William. 



•06 



■07 



•09 



•04 



•05 



•06 



•11 



•23 



•11 



•07 



•04 



•10 



•09 



Group IV.— 































Temperature Differences, 































1 8° '0 or greater . 



Ben Nevis. 



•37 



•41 



•19 



•24 



•24 



•30 



•31 



•37 



•48 



•48 



•58 



•53 



•38 



Do. do. do. 



Fort- William. 



•13 



■12 



•07 



•08 



•07 



•10 



•08 



•11 



■18 



•20 



•20 



•15 



•12 



As regards the rainfall, the observations give for all differences of temperature a 

 mean daily rainfall for the year of 0"40 inch for the top, and 0*19 inch for Fort- William, or 

 about half the amount of what is collected for the top, this being nearly the average 

 difference. But when the differences of temperature are only 12 o, or less, the daily mean 



