196 MR ALEX. BUCHAN ON THE STORMS OF WIND WHICH OCCURRED 



great fall took place to the S.W. To so great an extent did this occur, that the 

 whole atmospheric system of Western Europe must be considered as having re- 

 treated on its course, and to have travelled from the N.E. to the S.W. As the 

 translation proceeded, the depression widened and deepened, and a new depres- 

 sion was formed. The depression near Shetland, circumscribed by 29-3 on the 

 10th, and measuring 410 by 250 miles, increased to 1100 by 550 miles on the 

 11th, and the pressure in the centre was two-tenths of an inch greater. The 

 isobarometric 29 5 had changed its position in a most remarkable manner. Its 

 distance from 29 3 was greatly increased in Great Britain, and a new storm (VI.) 

 was formed in the interval, 300 miles in diameter, having its centre near Plymouth. 

 A little to the north of this, a space of about the same extent was noted for its high 

 temperature on the 10th. The isobarometric 29 • 7 had also changed to a position 

 equally remarkable, leaving a large space between it and 29 5 from Sardinia 

 northwards ; and in the interval a depression was formed round Genoa. On the 

 12th the two northern depressions had coalesced, and the isobarometric 29*3 con- 

 tracted to a fourth part of what it was on the 11th, and the whole driven back- 

 ward toward the N.E. The southern depression had travelled to the N.W., tripled 

 its area, and was one-tenth of an inch lower. 



The storm in the beginning of December will be afterwards described under 

 the head of the " Direction of Storms." 



Form of Storm Areas. 



The forms of forty-two different areas circumscribed by the isobarometric 

 lines admitted of examination. Of these, thirty were either circular or slightly 

 elliptical. In ten cases, the major axis of the ellipse was nearly double the length 

 of the minor axis, and in one case it was three times the length. In two in- 

 stances, 29-5 on the 11th November, and 29 3 on the 3d December, the outline 

 of the areas was very irregular, owing to the occurrence of two central depres- 

 sions in one case, and three in another, within it. It follows from this, that the 

 storms most commonly assumed a circular or oval form, and that the ellipses 

 were seldom much elongated. 



The area over which the storms spread themselves was very variable in size, 

 being seldom less than b'00 miles across, but often two or three times that 

 amount. This area was not constant, even as regarded the same storm from 

 day to day, but varied in size, sometimes contracting and sometimes expanding. 

 If it contracted, the central depression at the same time gave signs of filling up, 

 and the storm of dying out. On the other hand, if the area widened, the central 

 depression generally became deeper, and occasionally was broken up into two or 

 more separate depressions, which appeared to become separate storms with the 

 wind circling round each, as shown in the maps for 11th November and 3d and 



