474 RUM. GENERAL DESCRIPTION. 



summits of Halival and Haiskeval seem, from various 

 points of view, to possess nearly the same elevations.* 

 The eastern group, including Halival, Haiskeval, and 

 Ben More, is almost perpetually involved in mist. If 

 the clouds descend on the Cuchullin hills of Sky, it rarely 

 happens that those of Rum, although so much inferior 

 in height, are free. To this is owing the great proportion 

 of rain which falls in the island, and hence also arises 

 in a great measure the moory and unprofitable state of 

 so large a portion of its surface. This property of arrest- 

 ing the clouds on their arrival from the western ocean, 

 depends partly on the absolute height of the mountains, 

 but still more on their insulated position ; as they form 

 the only high land that lies between Sky and the moun- 

 tains of Mull ; both equally noted for the torrents of rain 

 which they precipitate on the surrounding country. It 

 is here that I have frequently observed a meteorological 

 phenomenon, which is also common in St. Kilda; namely, 

 that appearance in the clouds which is termed parasitical. 

 The general causes of this phenomenon have been often 

 discussed by philosophers; but having on one occasion 

 observed it to be attended with particular circumstances, 

 it will not be superfluous to describe the appearances 

 then witnessed. 



Those who have travelled in mountainous countries 

 must have often remarked that, even in a strong wind, 

 a cap of mist will frequently involve the summit of a 

 single hill : appearing to be in a state of absolute rest, 

 while the neighbouring clouds are sweeping rapidly along 

 under the influence of the gale. This appearance has 

 sometimes been attributed, either to the existence of par- 

 tial currents of air, or to some peculiar electrical condition 



* As there is no other map of the island than the sea chart, I have 

 been obliged to give such a sketch of the ground as could be made by 

 the eye, without which the place* and relations of the rocks that form 

 it would be unintelligible. 



