METEOROLOGY OF BEN NEVIS IN CLEAR AND IN FOGGY WEATHER. 471 



0'590 in. in April. The highest daily mean is 1*286 in. in September, and next to it 

 comes February with 1 # 270 in., and October with 1'163 in. April, May, June, July, 

 and August are all under the mean for the year, which is 0'998 in., or almost exactly one 

 inch. When it is remembered that in foggy weather the air is always saturated, and 

 besides that it has disseminated through it particles of water, which form the fog, on 

 which the vapour can immediately and without resistance condense, and that in summer 

 there is a much larger percentage of water vapour present in the atmosphere than is 

 found in winter, it appears somewhat remarkable that the summer rainfall per foggy 

 day should be so much lower than that of winter. When we turn to the maximum 

 rainfall of any foggy day in each month during the thirteen years, we find these same 

 months below the average again. The absolute maximum for the thirteen years falls 

 on the 3rd October 1890, when 7*287 ins. fell in the twenty-four hours; the next 

 highest value, 6*668 ins., falls on 6th February 1894, and the maximum rainfall on a 

 foggy day is above five inches in December, January, and March. The greatest fall 

 in one hour occurred between fifteen and sixteen hours on 14th January 1890, when 

 0*850 in. fell. 



The following short table puts together concisely the results of the rainfall measure- 

 ments in the two kinds of weather, and shows clearly the great contrast between them 

 in this respect : — 



Month. 



Clear Weather. 



Foggy Weather. 



Number 

 of Hours. 



606 



1,158 



1,335 



1,728 



2,228 



2,895 



1,502 



971 



1,296 



951 



983 



697 



Total 



Rainfall 



in Month. 



Mean Rain- 

 fall per 24 

 Hours. 



Number 

 of Days. 



Total Rain- 

 fall in Month. 



Mean 

 Rainfall 

 per Day. 



Maximum 



Rain lit 11 in 



one Day. 



Date of 

 Maximum. 



January, . 



February, . 



March, 



April, 



May, 



June, 



July, . 



August, 



September, 



October, 



November, 



December, . 



Inches. 



0-004 

 •033 

 •003 

 •110 

 •392 

 1-243 

 0-169 

 •720 

 •0-16 

 •064 

 •076 

 •000 



Inch. 



0-00015 

 •00069 

 •00005 

 •00153 

 •00422 

 •01030 

 •00270 

 •01777 

 •00085 

 •00161 

 •00185 

 •00000 



86 

 54 



78 

 59 

 27 

 42 

 46 

 58 

 79 

 64 

 88 

 66 



Inches. 



93-029 

 68-587 

 82-602 

 34-782 

 20-555 

 32-579 

 41-452 

 55-852 

 101-646 

 74-438 

 91-660 

 71-049 



Inches. 



1-082 

 1-270 

 1-059 

 0-590 

 0-761 

 0-776 

 0-901 

 0-963 

 1-287 

 1-163 

 1-042 

 1-076 



Inches. 



5-476 

 6-668 

 5-210 

 2-530 

 2-880 

 2-108 

 2-337 

 3-483 

 4-930 

 7-287 

 4-294 

 5-340 



Day. 



29 



6 

 11 

 22 

 15 

 16 

 13 

 29 

 31 



3 

 28 

 12 



Year. 



'92 

 '94 

 '90 

 '90 

 '92 

 '97 

 '90 

 '92 

 '91 

 '90 

 '93 

 '85 



Sums, 

 Mean, 



16,350 



2-860 



0-00389 



747 



768-231 



0-998 



4-379 







Barometric Pressure. — Next to the rainfall, the most striking difference between 

 clear and foggy weather on Ben Nevis is shown by the large and continuous 

 excess of pressure in clear weather over that in foggy weather. At every hour of 

 the year, without a single exception, the mean monthly pressure is several tenths of 



