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XXXI. — The Meteorology of Ben Nevis in Clear and in Foggy Weather. 

 By J. Y. Buchanan, F.R.S. (With Eight Plates.) 



(Read July 3, 1899.) 



The publication by the Royal Society of Edinburgh in 1890 of the hourly observa- 

 tions made at the observatory on the summit of Ben Nevis along with corresponding 

 observations at five different hours at Fort- William at the sea level was an important 

 contribution to meteorological science. As I held at the time the Lectureship in Geo- 

 graphy at the University of Cambridge it furnished a welcome supply of facts for the 

 illustration of important points in physical geography. What struck me most at the 

 time in the study of this work was the unique character of the observatory of Ben Nevis 

 itself, without reference to its companion at the sea level, as a first-class observatory 

 in a locality where the atmosphere is for the greater part of the year completely 

 saturated with moisture. Being also situated on a true peak, and that the highest 

 point in the British Islands, the observations may fairly be taken to represent the 

 meteorology of the clouds, or at least of such clouds as are in contact with moun- 

 tain slopes, and in any case they must afford rich material for the study of the 

 physics of the atmosphere. 



The weather on Ben Nevis falls naturally into three categories : the first includes the 

 days when the mountain is continuously enveloped in fog or cloud, the second, those 

 periods when the mountain is clear of clouds, and the third, periods during which 

 frequent alternations of clear and foggy weather occur. It seemed to me that 

 the conditions would be best understood by studying the continuously clear 

 weather and the continuously foggy weather, each by itself, and that this would 

 make it more easy to understand the conditions of mixed weather. When the 

 meteorological observations on Ben Nevis are looked at as physical observations, 

 and the object is to study the physics of the atmosphere, apart from all considera- 

 tions of weather, then a separation such as that above indicated becomes an obvious 

 preliminary. Had meteorology been first practised in the Tropics it would now be 

 in a more advanced state than it is. The meteorology of Europe, like the tides on 

 its coasts, is the most intricate and involved that can be found anywhere in the world, 

 and it is the worst possible material on which the study could be commenced. Within the 

 Tropics, and round the Poles, the conditions are simple and uninvolved, and the meteoro- 

 logical observations, at least those made within the Tropics, reflect this simplicity. 

 Generally, in the Tropics there are two kinds of weather, indicated by the terms Dry 

 season, Rainy season. In the Indian peninsula, for instance, during the months 

 December, January, February, March, and April, hardly a drop of rain falls, there 

 is little cloud, the air is very dry, and the temperature shows considerable daily range. 



VOL. XXXIX. PART III. (NO. 31). 6 F 



