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



of $ 2, because of the blowing of both currents being so fully 

 pointed out, that I cannot pass it over. We see that on 

 the south the south wind is prevalent and strong, and the 

 north is blowing as a fresh breeze in the north, the two cur- 

 rents meeting and balancing one another a little to the north 

 of the centre of the field of observation, and yet in this 

 place the barometer falls, the fall increasing towards south 

 on account of the greater height of the barometer there at 

 its commencement; but at the same time a rise takes place 

 in the north. Now it is certain that if these winds were 

 simply the flow of exactly similar currents, the one flowing 

 from north and the other from south to a space between 

 them, on this space the barometer would rise. What then 

 becomes of the air brought to the place of meeting if the 

 southern current does not carry it off in the upper regions of 

 the atmosphere, as shown in fig. 1 by the upper arrows be- 

 tween c and b ? That it does not arise from any atmospheric 

 change, originating in a central portion, such as a change in 

 the elasticity of the atmospheric columns, causing a portion 

 of air to roll off from their upper parts and a current to set 

 in towards their bases, is very evident, because the diminution 

 of pressure begins and is greatest at the most remote parts of 

 the south wind flowing towards it; but if we admit the ex- 

 planation given by § 2, the phenomena presented by the 

 barometer are perfectly consistent with the action of the two 

 contrary currents, which appear to have met so directly that 

 a calm, or a state of the air nearly approaching to it, is pro- 

 duced*. 



On the afternoon of the 1 3th the north wind becomes the 

 most prevalent, and the barometer rises rapidly throughout, 



* As the north and south winds are deflected, the one from east and 

 the other from west, the relative position of England and Scotland might 

 at first sight give rise to the opinion, that when the north was blowing in 

 Scotland and the south in England, they do not blow in opposition to each 

 other, but in parallel bands; in the cases of the 13th and 15th, however, 

 as well as others in which this opposition has been remarked, the observations 

 in Ireland and the extreme west of England remove all doubt as to the 

 actual collision of the currents, for we see by these the two currents blow- 

 ing directly towards each other in the more remote parts, and variable 

 winds, calms, or the deflections of the south current from east, near the 

 place of meeting. 



It is evident, however, that when the north-east wind prevails in a much 

 greater degree on the eastern parts than on the western, as appears to be 

 the case in some days of this period, the opposite currents may blow in par- 

 allel bands for some distance ; but on the parts immediately adjacent to 

 the north wind, the south wind will be south-east ; hence a northern loca- 

 lity may have a south-east wind when a north-east blows on a southern 

 one more to the east, a case frequently occurring in this country, as on the 

 2nd and 3rd. 



