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Hie Inter-relations of Barometric Pressure, Temperature, Humidity, Rainfall, Cloud, 

 Sunshine, and Wind, illustrated by the observations made at the two Ben 

 Nevis Observatories. (First Paper.) By Alexander Buchan, LL.D., F.R.S. 



The two Ben Nevis Observatories were in operation long enough to yield, from a 

 discussion of the work done at them, conclusions of very great value in meteorology. 

 Their records supply a complete set of hourly observations at the summit of Ben Nevis 

 from December 1883 to October 1904, or for a period of nearly twenty-one years, and 

 a complete set of simultaneous hourly observations in Fort-William from August 1890 

 to October 1904, or for a period of nearly fourteen years. 



These acquisitions to our knowledge of the atmosphere have been made under 

 conditions which are exceptionally favourable, since the Observatory at sea-level is less 

 than five miles distant in a straight line from the Observatory on the summit, and yet 

 placed close to the sea and in a fairly open situation. Moreover, it is not a valley 

 station, thus giving an enhanced value to the observations made there, as securing 

 practical immunity from the effects of nocturnal and diurnal air currents. In truth 

 there are no other two associated observatories or stations in the world, one at a high 

 and the other at a low level, where such favourable conditions exist. 



The geographical position of Ben Nevis is also favourable. In winter the British 

 Islands have a higher mean temperature than any other part of the land surface of the 

 globe equally far north, and consequently it is easier to live and work in these islands 

 than anywhere else in similar latitudes. All other mountain stations are either in the 

 Tropics or in the belt of high barometric pressure which occupies the southern portion 

 of the Temperate Zone. Ben Nevis, however, is clear of this high-pressure region, and 

 lies on the outskirts of the great barometric depression in the North Atlantic, which, 

 especially in the winter months, dominates the weather of North- Western Europe. 

 From Ben Nevis, therefore, we get data of observation which no other high-level 

 station yet established is in a position to supply to forecasters of the weather of North- 

 western Europe. 



The first large work the Directors of the Observatories set themselves to do was the 

 preparation of the meteorological ' constants ' of the mean hourly pressure, temperature, 

 humidity, sunshine, clouds, winds, and rainfall. These have been chiefly prepared by Mr 

 Omond, first for the Observatory at the top of the mountain, from January 1884 to 

 December 1903 ; and, secondly, for both Observatories, from January 1891 to December 

 1903. These ' constants ' are given in a series of tables for the months and the year, which 

 are published in this volume of the Ben Nevis Observations (see p. 481). In preparing 

 these constants, lines of inquiry were soon suggested, along which researches were 



TRANS. ROY. S0C. EDIN. — VOL. XLIII. 3 S 



