ON METEOROLOGICAL OBSERVATIONS ON BEN NEVIS. 179 
The above diagram represents the curve of this equation, and the points 
numbered from 1 to 12 are the twelve tabular places, beginning with 
May and ending with April. The curve evidently satisfies the observations. 
The relative mean readings of the thermometer are approximately 
represented by 
4 T=sin a; 
but the deviations from the true curve are greater than in the first case. 
Comparing the two expressions, the barometric differences are seen to be 
proportional to the increments of the mean temperature of the two 
stations. Accordingly, when the places of the table of barometric 
differences are laid down as co-ordinates to the places of the temperature 
able, the points are found to lie in approximately straight lines. One 
would have expected a less simple relation between the quantities in the 
wo tables. 
In consideration of the successful arrangements which have been 
made to minimise the effects of solar and terrestrial radiation at both 
the high and the low level observatories, and their close proximity to 
each other, the above result may be regarded as the most important 
datum hitherto contributed by meteorology for the discussion of inquiries 
dealing with the relations of height to pressure and temperature in the 
free atmosphere. The same consideration gives also a peculiar value to 
the table of corrections, empirically determined from the observations, 
for the reduction to sea-level of the barometrical observations at the top, 
calculated for every tenth of an inch of the sea-level pressure, and every 
bwo degrees of mean temperature of stratum of air, 4,407 feet thick 
between the two observatories. 
The mean annual differences of temperature of the top and bottom of 
® mountain, calculated from (1) the mean monthly temperatures, (2) 
@ highest mean monthly temperatures, and (3) the lowest mean 
honthly temperatures, are respectively 15°°9, 15°-5, and 16°-0. The 
maller difference obtained from the highest monthly temperatures was 
‘entirely caused by the unusually high temperatures at the top of the 
mountain during the anticyclonic weather that prevailed in the Junes of 
$87 and 1889, in which from the prevailing strong sunshine the whole 
nountain was in a sense superheated. 
During these years the mean annual rainfall at the top is 130-02 
inches, and at Fort William 74°74 inches. At the top the maximum 
monthly mean is 18-00 inches in December, and the minimum 5°35 inches 
a April ; whilst at Fort William there are 9-82 inches in December and 
#20 inches in June. The monthly differences are very striking, being 
y 153 inch in April, but 8-18 inches in December. As holds gene- 
ally in the north-west of Scotland, the rainfall shows a steady droop 
the minimum in June, but on the top of the Ben the minimum is 
eached in April, and by midsummer has risen considerably above it, 
me, in all probability, to a more copious precipitation from the ascending 
currents of the warmer months of the year. 
_ The mean monthly differences for the year between the rainfall at the 
top and bottom of the mountain, calculated (1) from the mean month] 
rainfall, (2) the greatest monthly fall, and (3) the least monthly fall, are 
respectively 4:61, 6:96, and 2:49 inches. The first of these means is 
approximately the mean of the other two, giving thus the curions result 
that in exceptionally wet months the difference between the rain-gauges 
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