Facts in Meteorology. 127 



The Harmattan is an east wind of great dryness, which visits the 

 western coast of Africa in the lovy latitudes, in the months of January, 

 February and March. It is probably the true trade wind, which or- 

 dinarily does not act in these regions as a surface wind, but passes 

 in a higher stratum. 



The Helm wind is a violent whirlwind, peculiar to the western 

 side of the Cross Fell mountain in Cumberland ; and it occurs only 

 during an easterly wind. Whirlwinds of the same character are not 

 uncommon in other regions where obstructions are presented to the 

 regular wind. 



Whirlwinds of great extent always act horizontally ; those of small 

 dimensions act either horizontally or vertically, or at any intermediate 

 angle of inclination. Many of this smaller class of whirlwinds occur 

 in the atmosphere which do not reach the surface of the earth, and 

 can be recognised only by the sensible phenomena which they pro- 

 duce. The most obvious of these characteristics are, the cloudy pipe 

 or pillar called the waterspout j thick masses of turbulent clouds ; 

 thunder and lightning ; often repeated or continuous thunder, or 

 lightning; a continued roar in the atmosphere resembling the noise 

 of a loaded waggon driven rapidly on frozen ground, or in some cases 

 lik« the continued discharge of artillery and small arms; hail of un- 

 common size in a circumscribed locality or running in veins ; large 

 drops of rain ; a deluge of rain falling in a small compass ; the falling 

 of sand, ashes, small fish, reptiles, and other matters previously taken 

 from the surface ; Si-c. &,c. 



Whirlwinds of whatever form or extent, and however active or vio- 

 lent their revolutions, move forward only with the velocity of the more 

 regul^r wind by which they are impelled. 



Showers of frogs, fishes, &c. arise from waterspouts, or spiral ed- 

 dies, [whirls] by which small portions of the waves of the sea and 

 ponds of water, (in a state of division,) with their contents, are forced 

 to an elevation ; and thus being transported to a distance, and there- 

 falling, produce these strange precipitations. 



In clear, calm, and sultry weather, whirlwinds have been excited 

 by fires, burning simultaneously in a large circle, and have exhibited 

 violent and continued electric explosions, and the peculiar phenome- 

 non of the turbo or whirling pillar, with other of the forementioned 

 characteristics. 



Volcanic eruptions often excite whirlwinds of great altitude, and 

 of most violent character. 



