274 Mr. W. Brown on the Oscillations of the Barometer. 



The elevation of the barometer indicated by the foregoing 

 observations, though gradually decreasing from the 4th, did 

 not subside till the approach of a storm from south-west 

 (§15); which began at the Orkney islands on the night of the 

 7th, was blowing at the island of Mull on the 8th, and arrived 

 at Glasgow at ii p.m. of the same day; in the north of Ireland 

 (Donegal) at 8 p.m.; and at North Shields (a little to the 

 north of Donegal in latitude, but on account of its more 

 easterly position later in receiving the storm) at a very early 

 hour on the morning of the 9th. The change of the wind as 

 the storm progressed is well-marked by the diagrams. On 

 the 7th, the wind remained north-east throughout the day in 

 almost the whole of England, but at the Orkneys had changed 

 to north-west (§ 18), and was variable at Mull island in the 

 evening: at North Shields it changed to north-west after 

 mid-day, and at night the storm began at the Orkneys from 

 south-west. On the 8th, the south-west wind is blowing in 

 the greater part of Scotland, whilst to the southward the wind 

 is still north, but in some cases north-west. In the evening 

 the changes before noticed take place, the wind being yet 

 northerly in the south. On the 9th the storm became pre- 

 valent throughout, on which day the barometer attained its 

 minimum in the north (§ 3), its height in the south being very 

 little reduced (§ 2), although it appears that on that day the 

 wind was blowing as strongly in the south as in the north 

 (§4). 



The approach of the storm from north is seen also by the 

 falling of the barometer, as indicated by the observations. At 

 North Shields the barometer attained its minimum (there 

 29-276) at 5 p.m., and at 9 p.m. it had risen (HO, though 

 reckoning simply from the extreme observation, it had not 

 risen at all ; whilst at Orkney it had risen 0*20, and in the 

 south it was yet falling (§ 3). On the morning of the 10th 

 the barometer at the Orkneys had risen 0*39, with a strong 

 gale from north-west (§ 3 and 12) ; but at Shields, from 5 p.m. 

 on the previous day to about the same hour on this, although 

 the barometer rose, the air was almost calm. The diagram, 

 however, together with the barometric heights, fully explains 

 this ; for we see that its position was that of the meeting of the 

 two currents, the north current blowing on the north and the 

 south one on the south (§11), the latter continued by the state of 

 the barometer ; the barometer rising however by reason of the 

 strength of the north wind setting in in the north (§ 6). The 

 north wind in the middle and southern parts of Scotland appears 

 (on account of the low state of the barometer at Orkney) to 

 arise from the impetus which it has received in blowing in the 



