Mr. W. Brown on the Oscillations of the Barometer. 27*7 



of the barometer at 9 a.m. was 29*30 inches, and at Orkney 

 the wind is from east, hence at the same distance on the west 

 of these islands the barometer is probably below this. If we 

 now suppose, whilst the wind is blowing as shown by the dia- 

 gram, the point C of fig. 3, by the motion of the line A C 

 (§ 16), to moye considerably northwards, and to be a little 

 to the north of Holyhead, where the wind is strong from 

 north-west, the phaenomena will be simply a particular case 

 of the general result of the paragraph, for the wind is strong 

 from north-west on the localities in the direction which 

 would be that of the line C A, and variable between west and 

 north-west at Flamborough-head, and west-north-west and 

 very light at North Shields, places, which with regard to the 

 figure would be nearly on a horizontal line with the point C; 

 and in the north, but not extending to Orkney (where the ba- 

 rometer is just beginning to rise), the wind is variable between 

 south and west, and extremely light; but at the locality near- 

 est to Orkney, Greenock, it appears to change to north-east 

 in the latter part of the day. This however is the extreme 

 portion of the storm, and accordingly, soon after this, the 

 north wind sets in briskly from north-east instead of from 

 north-west. 



It may be observed that in the south the rise of the baro- 

 meter ceases at Cork whilst it continues at Plymouth; the 

 phaenomena of the next day (13th) however, explain this, for 

 by the setting in of the current from north-west on the south- 

 west, which opposing the south wind blowing in the more 

 southern parts, causes a very rapid rise of the barometer in 

 the south, but more especially in the south-west, a dispro- 

 portionate pressure there is again produced, and the conse- 

 quences are in some degree the same as before ; for on the 

 13th, although the barometer rose rapidly at the Orkney 

 islands, and the north-east wind fully set in in Scotland, the 

 south wind blowing previously only in the extreme south, in- 

 creases in strength and becomes prevalent in all the southern 

 part, causing a considerable fall of the barometer in the south, 

 which, as before, occurs first at Cork, confirming the view 

 that the rarefaction of the atmosphere is greatest in the north- 

 west. At North Shields, where on the night previous the wind 

 was strong from the west, it changed to south-west, though 

 extremely light, and caused a slight fall of the barometer be- 

 tween 9 a.m. and 2 p.m. 



The phaenomena presented by the diagrams of this day, 

 together with the variations of the barometer given in the 

 first column of the 13th, though of the same kind as in two 

 previous instances, afford so striking an example of the case 



