Mr. W. Brown on the Oscillations of the Barometer. 275 



extreme north, together probably with a higher barometer on 

 the east (shown by its easterly deflection) : thus we find the 

 wind decreases in strength as it advances, being at Mull is- 

 land only brisk. The equality in the force of the two currents 

 is not however of long continuance, for that of the south wind, 

 evidently because of the great depression of the barometer in 

 the north below its height in the south (Orkney, barometer 

 28*70, London 29'81), on the 9th, greatly increases and ad- 

 vances as a storm towards the north. But this difference of 

 the atmopheric pressure requiring, on account of the great 

 distance of the localities of the extremes of pressure, and the 

 resistance of the opposite current blowing in the north, a long 

 interval of time to produce its effect, does not arrive at North 

 Shields till the latter part of the 10th as a S.E. or rather S.S.E. 

 storm (being deflected by its collision with the contrary cur- 

 rent) (§11 and 16), and continues until about the same time 

 of the 11th. 



In the phaenomena now before us we have a good example 

 of an advancing portion of a storm (§ 16). The fall of the 

 barometer, which continues in the south whilst the rise is 

 going on in the north, increases on the 10th, and advances, 

 together with the wind, towards the north, where, excepting 

 in the extreme north, it falls to a greater degree than before, 

 and, as noticed in § 16, the greatest depression is in the 

 south. The progressive motion of the storm may however be 

 traced in both the directions of the figure of § 15, but the 

 south-east movement is in the south : thus at Cork and Ply- 

 mouth the minimum depression occurred on the evening of 

 the 10th, at Bristol about noon of the 11th; for out of four 

 observations that at noon was the lowest (2999); and at Paris 

 (south-east) and at North Shields (north-east) it happened 

 simultaneously about 9 p.m. Hence if we suppose Cork to 

 represent the point C, fig. 3, then the line c C prolonged 

 would extend to Paris, the storm however diminishing in in- 

 tensity, and the line C B from Cork to North Shields. The 

 limit of this storm may be observed in the north; for at Orkney 

 the wind continued northeast, and at Mull island east, but 

 yet the barometer at Orkney falls, though during a north- 

 east wind, but not to so great a degree as the next station 

 (Glasgow) (§ 5), for on the next day (the 12th) the minimum 

 depression, or the point C, was in the south of Scotland or 

 north of England ; hence Orkney would represent the point 

 E. of fig. 1. 



The diagrams of the 10th and 11th (Plate VII.) are also 

 of interest as regards the deflection of the currents produced 

 by their meeting: on the north the wind is N.E., in the south 



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