N. 



N.E. 



E. 



S.E. 



s. 



s.w. 



w. 



N.W. 



Calm. 



4 



36 



44 



26 



23 



22 



10 



4 



13 



AND THE PREVAILING WINDS OVER THE GLOBE 593 



part, in a course lying somewhere between Iceland and Faro ; as a consequence 

 of this, and of the mean low pressure in the north of the Atlantic in the winter 

 months, the prevailing winds in Great Britain at this season are south-westerly, 

 and even in stormy weather the wind seldom veers further towards the north 

 than N.W., and continues only for a short time in this quarter. To these con- 

 siderations we owe the mildness and equableness of the winter climate of Great 

 Britain. At Stykkisholm, in the north-west of Iceland, which lies on the north 

 side of the storms' path, the great preponderance of winds in the six stormy 

 months, from October to March, are N.E. and E., as will appear from the follow- 

 ing Table, which gives the number of days on an average of the three years, 

 1866-69, winds from the different points have blown during these six months: — 



Number of days the wind has blown . 

 at Stykkisholm, from October to 

 March, on an average of three 

 years, viz., 1866-69, . . J 



Suppose a change in the distribution of land and water took place in this 

 part of the globe ; on the one hand, land taking the place of sea to the west of 

 a line drawn through Spitzbergen, the north of Norway, Faro, and the east of 

 Newfoundland ; and, on the other hand, sea taking the place of land over part of 

 the north of Africa, and over the comparatively low plains of Europe and 

 Siberia, the following changes would take place in the distribution of atmo- 

 spheric pressure in winter: — The high pressure over Asia would be reduced 

 and contracted ; the high pressure in North America would be increased and 

 extended, so as to include Greenland ; and the low pressure round Iceland would 

 be transferred to the south-east, so that the central space of least mean pressure 

 would probably stretch from the north of France to the Gulf of Finland. Under 

 these new conditions, mean pressure would increase greatly from the south of 

 Great Britain towards the north-west, and thus northerly and easterly winds would 

 become the prevailing winds in winter ; and as the mean central track of storms 

 would lie in a line from the north of France to St Petersburg, the winds accom- 

 panying storms, particularly those in the rear of the storms, would be dry and 

 intensely cold. Further, suppose the Gulf Stream, or any oceanic current from 

 equatorial regions, to flow past Great Britain on its way to the Arctic Ocean, 

 through the Baltic and White Seas, from the lower mean temperature which 

 would be brought about by the now prevailing northerly winds, the vapour 

 brought by the Gulf Stream would be precipitated no longer in the form of rain 

 but of snow, and frost would be of frequent occurrence. Since the heat of summer 

 would be insufficient to melt this snow, it would accumulate from year to year ; 

 and thus the Gulf Stream, instead of ameliorating the climate, as at present, 

 would only the sooner and more effectually, by accumulations of snow and ice, 

 bring back to the British Islands the climate of the glacial epoch. 



