INTER-RELATIONS OF BAROMETRIC PRESSURE. 507 



The Table of Corrections extends from 4*902 inches to 4*176 inches. The fractional 

 parts of an inch only are given in each column, it being unnecessary to repeat the 4* 

 inches, which is placed at the top and is common to the whole Table. When the Table 

 was constructed the only instances of very low pressures that had occurred were 

 accompanied by low temperatures ; aud as a rule high temperatures were associated 

 with high sea-level pressures. The Table therefore only extends as low as 27*400 inches 

 up to a mean temperature of 28° ; it stops at 27 "600 for the next two degrees, at 28*000 

 from 31° to 45°, at 28*500 from 46° to 60°, and at 29*000 from 61° to 75°. This Table 

 has been used to reduce the readings of the Ben Nevis barometer at every hour of each 

 day for the period of over thirteen years embraced by this discussion, and the limits of 

 the Table have included all cases except a few at very high pressures, viz. 31 inches and 

 upwards, and some at temperatures below 16°. For these it was easy to extend the 

 Table by extrapolation, and the general law that a wide range of pressure is only needed 

 at low temperatures, and that high temperatures are associated with high pressures, has 

 been found to hold good throughout. It is, however, necessary to bear in mind 

 that the figures of the Table do not take into account diurnal and seasonal variations. 



The first step taken in dealing with the observations was to enter on sheets, one 

 sheet for each day, the hourly values : for the barometer, the mean pressure at 

 Fort-William at 32° and sea-level, the mean pressure at Ben Nevis at 32° — this 

 reduced to sea-level from the Table — and then the difference of these sea-level 

 pressures ; for the temperature, the temperature at Fort- William and at Ben Nevis, 

 the mean of these two temperatures, and the difference between them ; for the 

 hygrometer, the depression of the wet blub below the dry bulb at Fort- William and at 

 Ben Nevis ; for the sunshine, the hourly amounts at each place ; for cloud, the amount 

 on scale to 10 for each place ; for rainfall, the amount in inches or decimals of an inch ; 

 and for wind, the direction on the top of Ben Nevis and its force on scale to 12. 



Such sheets have been prepared for each day from the opening of the Observatory 

 at Fort- William to December 1903, and it is from this source that the data employed 

 in this discussion have been obtained. Several examples of these, in whole or in part, 

 follow, as representative of the anticyclonic type of weather, the most prominent 

 meteorological conditions accompanying which is a small difference of the mean daily 

 temperature between them ; and the cyclonic type, which is accompanied with a large 

 difference of their mean daily temperatures. 



The Anticyclonic Type of Weather. — On 29th September 1895 temperature rose 

 higher at many places in Scotland than had been recorded in this month for upwards 

 of half a century. This was accompanied with skies all but absolutely cloudless, and 

 it is noteworthy that they were accompanied with unwontedly heavy dews in the 

 mornings, and with calms or very light winds. 



