20 



Ben Nevis have lately sliown ttat over a surface low pressure 

 area there exists a relatively high-pressure region, caused by the 

 accumulation of the air in higher regions, carried upwards by the 

 warm ascending currents ; and especially must this be the case 

 at great elevations in low latitudes. We have but a faint idea of 

 the actual force of that eruption. It would at any rate carry 

 volcanic dust far into the higher atmosphere, and land it safely 

 on the high-pressure zone existing high over the calm belt. 

 Bear in mind now that a similar high-pressure area existed in 

 the upper atmosphere over the surface low-pressure areas of 

 India and Central Asia ; and that the tendency of motion of this 

 lofty high-pressure was towards the southern hemisphere, where 

 a general surface high-pressure existed, overtopped, as in the 

 case of all surface anticyclones, by a relatively lower pressure. 

 Thus currents from the upper atmosphere of Southern Asia 

 would flow southwards to preserve equilibrium, and feed the 

 surface high pressure of the southern hemisphere at that 

 season of the year. These currents would (but only for a 

 short time on account of its proximity) hinder the dust from 

 approaching India, and would carry it southwards, causing the 

 *' red glows" to be experienced earlier in Australia and South 

 Africa, for instance, than in European latitudes. But I have 

 still to offer some explanation of the fact of the "red glow" 

 phenomena travelling due west, via the Seychelles, Cape Coast 

 Castle, and Trinidad, at the rate of nearly 70 miles an hour, 

 reaching the latter place, 11,700 miles away, within a week. I 

 see no way at present of accounting for this, but on the theory 

 that, owing to the rapid rotation of the earth at the equator, 

 viz., 507 yards a second, or 1,038 miles an hour, the higher at- 

 mosphere in equatorial region lags behind, causing a strong cur- 

 rent to set westwards from the same causes that explain, for in- 

 stance, the phenomena of the north-east and south-east trade 

 winds ; and the circulation of the tides assisted by the earth's ro- 

 tation as a secondary result of the moon's attractive influence. 

 This equatorial east wind, if such exists, is in the high-pressure 

 zone over the calm belt, and sends oft' branches to northward 

 or southward of the Line respectively to maintain the great 

 systems of surface anticyclones in either hemisphere, according 

 to the geographical distribution of land and water and the 

 season of the year. 



The objection that more dust should have been expelled to 

 spread so widely will not hold in my opinion, as we have but a 

 faint idea of the vast amount actually expelled and diffused 

 by the currents as impalpable powder. 



Lastly we have one common objection to the main dust 

 theory, viz., How can the matter remain suspended for such a 

 long period in opposition to that force which we call gravity ? 



