Dove on the Law of Storms. 335 



Let us now consider these storms on their entrance into the 

 temperate zone. Their change of direction from S. E. to S. W., 

 on passing the outer boundary of the trade winds, has been ex- 

 plained on the assumption of the storm meeting with S. W. winds, 

 instead of the N. E. wind which had till then opposed its advance. 

 It must however be remembered, that the direction of the wind 

 in the temperate zone is not constant but varying. Such phe- 

 nomena as those which have been described require for their oc- 

 currence, that the S. W. winds do actually predominate previous- 

 ly in the temperate zone : barometric minima accompanied by 

 storms are therefore only observed when those conditions are ful- 

 filled. They were so in a high degree previous to the time of 

 the minimum on the 24th of December, 1821 ; for in November 

 and December the mean direction of the wind had been south- 

 west in Penzance, London, Bushey, Cambridge, Lancaster, Man- 

 chester, Paris, Brest, Dantzic, Konigsberg, &c. ; and it appears 

 from the Bibliotheque U?iiver$elle, that a more or less stormy 

 southwest wind prevailed throughout the middle region of west- 

 ern Europe. 



We have before assigned reasons for the sudden increase of 

 breadth and diminution of intensity which accompany the change 

 of direction of the course of the storm. It will be seen by the 

 converse of the same reasoning, that the intensity increases again, 

 when smaller whirlwinds are, from any cause, developed from 

 the larger one. Such was the case in the Mediterranean at the 

 time of the minimum of the 21st of December, already noticed, 

 when the advancing masses of air, arrested in their progress by 

 the Spanish mountains and by the Maritime Alps, were set into 

 violent rotatory motion around these points as fresh centres; and 

 we find accordingly that the force of the storm was particularly 

 great there no less than at the primary centre. In regard to the 

 latter, the Brest accounts say, on the 26th of December, u We 

 have been living for fourteen days in the midst of storms, which 



5 with unparalleled fury." In London 

 there was the highest flood which had been seen since J 809. 

 At Portsmouth one gust from the S. S. E. is spoken of as almost 

 unprecedented, and the sea rose to an enormous height. In re- 

 gard to the secondary centres, the ravages of the storm in and 

 around the Mediterranean were very great. From Leghorn to 

 Barcelona it was terriblv destructive. On the southern declivity 



