328 Aérial Currents shown by Volcanic Ashes. 
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The course of the great aérial stream into the Atlantic basin, | 
after crossing the equator from the southern hemisphere, is seen 
from other evidence than the reported courses of the clouds, and . 
occasional surface winds. We learn from Humboldt, that in the r 
great eruption of Jorullo, a volcano of southern Mexico, which is 
2100 feet above the sea in lat..18° 45’, lon. 101° 30’, the roofs 
of the houses in Queretaro, more than 150 miles N., 37° E. from 
the volcano, were covered with the volcanic dust. In January, 
1835, an eruption took place in the volcano of Cosiguina, on the 
Pacifie coast of Central America,.in lat. 13° N., and having an 
elevation of 3800 feet, the ashes from which fell on the island of 
Jamiaca, distant 730 miles N. 60° E. from the volcano. «The 
elevated currents by which voleanic ashes are thus pape sa 
are seldom or never of a transient or fortuitous character, 
these results therefore afford us one of the best indications of their 
general course. 'Thus the progress of the higher portion of the 
trade wind was marked by the eruption of Tuxtla, lat. 18° 30, 
lon. 95°, which covered the houses in» Vera Cruz with ashes, at 
the distance of 80 miles, N. 55° W. and also at Peroté, 160 miles 
N. 60° W. The ashes from the‘ volcano at St. Vincent, which 
fell at Barbadoes and east of that island in 1812, mark the course’ 
of a current from the westward, which appears there at times, i 
the region of clouds, and may perhaps be connected — with the 
permanent winds on the Pacific coast of Mexico. Few - factsin j 
meteorology are more worthy of our attention than the stratiform : 
character and the vast horizontal extension of the serial: cunentsy 
in different portions of the globe.* = 
Over the United States and the temperate ‘aeiendes of the! At 
lantic the course of this great southwest current is strongly mark 
ed both by the movements of the clouds and the general course 
of the surface winds, notwithstanding the degree of obscurity 
which is induced by the generally revolving character of* the 
lower winds ; for even the northeasterly and northwesterly winds 
are found comprised in a general movement of the lower atmos- 
el towards the northeast.t elaies we find’ the great ¢ om 
see ¢ Chartal aah ly. 
resulis of seven years’ observations on the courses “of the. donde wd _ 
winds, at New York, see ope bac ib i Ser., nigcntreasit ; 
oe tep, gate str! “eeny ae ni ae 
at 
