338 Dove on the Law of Storms. 



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. xm f ) 

 I have considered in detail a case of this kind, in which a north 

 wind blowing directly against the southwest 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 phenomena 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 

 current forces its way underneath, the falls of snow are immedi- 

 ately followed by fresh cold advancing from N. E. to S. W. 



When navigators are overtaken by a rotatory storm, the follow- 

 ing are practical rules for escaping from its influence as soon as 

 possible : 



L In the northern temperate zone : — If the gale begin from 



W 



for 



If, on the con- 



trary, it begin from the N. E. and change through N. to N. W., 

 the vessel should steer northwestward, for she is in the north- 

 western half of the storm. 



2. In the northern part of the torrid zone ; — If the storm set 



in from the N. E. and the wind change through E. to S. E., the 



