96 Baron Von Buch's Observations on 



but no one will easily be induced to go from Teneriffe to Cana- 

 ry or Madeira, for he would run the risk of consuming a whole 

 month in the attempt. Few people on the globe live more soli- 

 tary than the inhabitants of Ferro. Only one day is required 

 to go thither from Teneriffe ; but the return, which can only 

 be effected by the help of strong and unusually far spreading 

 land-winds, is so insecure and dangerous, that people only make 

 this voyage when it is absolutely necessary. Generally, eight or 

 ten days are calculated upon ; but it may happen that three, four, 

 or five weeks, will be required. 



The manner in which this north-easterly trade-wind is, to- 

 wards winter, supplanted by that from the south-west, is very 

 singular, as well as instructive, and of the greatest importance to 

 the science of meteorology. These winds do not previously 

 prevail in the south, and then advance towards the north, as, 

 from their direction, might at first be imagined ; but, as has been 

 before remarked, they appear sooner on the Portuguese coast 

 than in Madeira, and there earlier than in Teneriffe and Canary ; 

 as if, from the north, they descend gradually from the upper 

 regions, where they were at all times, even during summer, 

 when the north-east trade-wind blew at the level of the sea with 

 the greatest violence. It was conjectured long ago, that there 

 might be, in the upper regions of the atmosphere, a current run- 

 ning in an opposite direction to that below ; and on this suppo- 

 sition was founded the generally received theory of the trade- 

 winds, viz. that which ascribes their origin to the rarification of 

 the air at the equator, and the rushing in of the colder air from 

 the north and south, which, having at first a course from north- 

 east to south-west, is at last entirely converted into an easterly ; 

 because in lower latitudes, the rotatory motion is greater than 

 in those from whence it proceeded. But this returning current 

 was, till of late years, only a conjecture. In 1812, a great volca- 

 nic eruption took place in St Vincent's. To the eastward lies 

 the Island of Barbadoes, at no great distance, but so decidedly 

 separated by the easterly trade-wind, that it could only be reach- 

 ed by making a circuit of many hundred miles. This east wind 

 brings to Barbadoes no rain and no clouds. All of a sudden, 

 however, dark clouds appeared over the island, and the ashes from 

 the volcano in St Vincent's fell in great abundance, to the great 



