NOTES ON SOME RECENT BAROMETRIC DISTURBANCES. 217 
Mr. Russett said: The cause of thunder-storms i is the meeting 
of the tropical and polar winds. The tropical is in summer 
dry wind, charged: with igus ones and -when a cold 
ich cannot take the whole 
charge, and the excess appears as Gueve discharges. Now, 
this meeting-ground of the two winds varies with the _— 
a hot summer the sth comes farther south, 
are in the latitude of the margin, and therefore in the latitude 
of thunder-storms; while in an ony year the mee 
ground of the two winds is nort and we have Fick 
storms. That the immediate cause is ‘this pene, I think, is 
proved by.an investigation I went into last year, when I fo und, 
ining 195 thun Ger-storns, that the two currents Langa 
ace 
whereas in hurricanes and smaller rev: olving storms the barometer 
always falls as the storm comes on, and rises as it goes off. Now. 
m America a theory has been ably put forward to account for the 
storms which are so frequent there. It has not been generally 
accepted, but it is in accordance with very many observed 
facts. According to this theory, when the tropical and polar 
currents meet, one passes above the other, and the actual plane 
of meeting is inclined to the surface of the ground, and the two 
surfaces are just in that condition when, in accordance with well- 
known laws, a vortex motion may originate from a small disturbing 
cause, such as an abrupt hill, and haying once thagyioas LT ahi els 
n in 
winds having the velocity of 70 or $0 miles per hou ur, as T have 
shown (“ — of New South Wales’) our upper currents 
to possess, travel forward as an independent mass, with a 
veloci i as I have shown this storm of November 27 to have 
had. We see ~_ sg vortices do sometimes form, by the havoc 
they — in passing through our forests, but whether such a 
gr ure 
exerted ona fluid i is cmon all over it, but when large spaces 
are concerned this takes time, and we know from many experi- 
