Facts in Meteorology. 127 
The Harmattan is an east wind of great dryness, which visits the 
western coast of Africa in the low 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; 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 aloaded waggon driven rapidly on frozen ground, or in some cases 
like the continued discharge of artillery and small arms ; hail of un- 
common size in a circumscribed loeality 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 ; &c. &c. 
Whirlwinds of icin form or extent, and however active or vio- 
lent their revolutions, move forward only with the veloeity of the more 
regular 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, produits these strange precipitations. 
n clear, calm, and sultry weather, whirlwinds have been Sxsted 
by fires, burning simultaneously i in a large circle, and have exhibited 
violent and continued electric explosions, and the peculiar phenome- 
non of the ¢urbo or whirling pillar, with other of the forementioned 
characteristics. 
Volcanic eruptions often excite whirlwinds of great alana and 
of most violent character. 
