ai3 



rents, at the ordinary elevation of cirri, as indicated by the motions of these 

 clouds, may be represented by the following figures : — 



No. of obserratkms. 



From points N.W. to N.N.E. inclusive 267 



N.E. to E.S.E. „ 8 



S.E. to S.S.W. „ 187 



S.W. toW.N.W. „ 49C 



958 

 It thus appears, that in this part of the world, the instances in which 

 the upper currents of the atmosphere move from the easterly points are 

 exceedingly rare and exceptional, being under one per cent., and even 

 the eight instances noted are open to objection, as in nearly the whole 

 of them the clouds observed, though of the cirrus type, appeared to move 

 at an elevation considerably inferior to that which such clouds usually 

 occupy. So far as I have observed, the instances of cyclones coming 

 over from these points are equally rare ; indeed, I have not as yetfoimd 

 a single example. 



Our heaviest storms generally have a progressive motion from S.W. to 

 N.E., and the most frequent tract of their centres, is a line passing in 

 that dii'ection across the North of Ireland, and the South of Scotland. 

 A great number of these storms are central in the Merse of Berwickshire, 

 hence the barometric range is greater in general here than at places situ- 

 ated to northward or southward. The damage done by such storms 

 is much greater at places situated within the range of the Southern semi- 

 circle of the whirl, at a certain distance from the centre, than at places 

 within the northern semicircle, or even in the course of the central line. 

 A remarkable instance of this was afforded by the memorable storm of 

 7th January, 1839. The centre of this storm passed in a S.W. to N.E. 

 direction, by Belfast, Dumfries and the Merse. The barometer here fell 

 rapidly with the wind at S.E., and rose with the wind from N.W., the 

 wind in passing through the westerly points having been comparatively 

 slight. In the southern semicircle of the storm, particularly at Dublin, 

 Liverpool, &c., the violence of the wind was much greater than at this 

 place, and was most furious from S.W. In the northern semicircle, 

 embracing the central and northern districts of Scotland, the wind blew 

 from the easterly and northerly points, and caused comparatively little 

 damage. The greater force of the wind in the southern semicircle is 

 readily explained by the consideration, that in it the maximum force of 

 the wind is composed of the vortical force plus the progressive, 

 whereas at the centre it consists of the vortical force only, and in the 

 northern semicircle, of the vortical minus the progressive. If we sup- 

 pose the vortical or rotatory vebcity of the wind, in a storm such as that 



