DOVE ON THE LAW OF STORMS. 919 
a remark which has been made by almost all observers who 
have carefully examined the connexion of the direction of the 
wind with the accompanying phenomena of the weather. On 
the north-western side of a rotatory storm the wind vane turns 
N.W., W., S.W.; the usual order, according to the law of rota- 
tion, being exactly opposite, 7. e. S.W., W., N.W. 
We thus see that the rotation of the earth on its axis causes 
three different phenomena:—1. The constant direction of the 
trade winds, and the regular alternation of the monsoons. 2. The 
regular order in the change of direction of the wind, which in 
both hemispheres is with the sun. 3. The rotatory movement 
of storms in a determinate order. 
The course of the phenomena which we have been consider- 
ing becomes very much complicated when the advancing storm 
‘meets another wind, or when it has successively to press aside 
currents of air from different directions. In treating of the mini- 
‘mum of February 2nd and 3rd, 1823 (Pogg. Annal., vol. xiii.), 
T have considered in detail a case of this kind, in which a north 
wind blowing directly against the south-west current, the meet- 
‘ing of the two produced a calm, which appeared to bear no sort 
of relation to the alteration of the atmospheric pressure. The 
minimum would seem to be divided into two portions by the cur- 
rent flowing towards its centre, so that there are two places of 
least pressure. The elucidation of these pheenomena requires the 
comparison of observations made over a very extended surface ; 
but as the view which I then took has been since confirmed by 
more complete data, I refer to it here. This case leads us on to 
the consideration of the phenomena which follow these great 
agitations of the atmosphere, when the equilibrium which had 
been violently disturbed re-establishes itself after the disturbing 
cause has ceased to act; but these secondary phenomena must 
not be confounded with the primary ones. North of the mini- 
mum there may often be found an unusually high barometer, ac- 
companied by severe cold and by heavy falls of snow at the limit 
of contact between the warm and the cold air. The falls of snow 
do not enter far within the precincts of the cold, but rather form 
a border along its limits. As long as the minimum repels the 
cold air, and causes it to accumulate, the falls of snow, succeeded 
by thaw, recede likewise towards the north; but when the polar 
eurrent forces its way underneath, the falls of snow are imme- 
diately followed by fresh cold advancing from N.E. to S.W. 
Q2 
