85 



Lecturer was prepared in a great measure to admit this, he also favoured 

 the theory that this stream was produced on the principle of an exchange 

 in specific gravities between the hot water of the tropics, and the cold 

 water of the polar regions ; but of late nearly all writers on the subject 

 had followed Sir Wyville Thomson, in attributing it to the action of 

 the trade winds. It was pointed out that any change in the ocean 

 currents in past ages must have produced a corresponding change in the 

 mean temperature of northern Europe. In a paper recently read before 

 the Geological Society on the geology of Barbadoes, by Messrs. Jukes 

 Brown and J. H. Harrison, these gentlemen had shown that the recent 

 geological deposits of that island proved that they were almost identical 

 in composition with the silicious and globigerinal ooze now found in the 

 depths of the Atlantic, and the conclusion they arrived at was, that the 

 whole of central America and the Carribbean region was deeply 

 submerged during the pliocene period, leaving free communication by 

 sea between the Atlantic and Pacific Oceans. This, the Lecturer 

 explained, would greatly alter the climate of Great Biitain by diverting 

 the gulf stream, if not destroying it altogether. Adverting to the 

 effect of prevailing winds, Mr. Dowker remarked that the relative 

 heights of the land was shown by geologists to have undergone great 

 fluctuations since the glacial epoch, and this again must have influenced 

 the climate, irrespective of astronomical changes. 



The Lecturer asked if it was not possible to trace some changes in 

 the climate of Great Britain since the Roman period ? The Romans 

 seem to have introduced vines into Britain, and vineyards were once 

 numerous, at present the climate does not seem to suit them. Our 

 seasons, he observed, were greatly influenced by the prevailing winds, 

 and were there not to be observed fluctuations in cycles of years in our 

 climate ? A change of wind occurring at the equinoxes was generally 

 followed by a continuance of prevailing winds blowing from the same 

 direction as when this took place; and the wind travelling round in an 

 opposite direction to the sun was characterised by cold summers, and it 

 was suggested that, inasmuch as the equinoxes influenced the wind in 

 the case of the monsoons, so the latter might have its rotary direction 

 altered at the same time, under certain astronomical conditions. 



The Lecturer was not able to give detailed facts explanatory of the 

 influences of the sun and moon on the wind currents ; but inasmuch as 

 their combined action influenced the water, he did not see why in the 

 same way they might not influence the air. 



It was briefly explained how the trade winds were affected by the 

 rotation of the earth, and by the sun's heat raising the air in equatorial 

 regions, and so causing an indraft of colder polar air towards the 

 equator. 



And the periodic winds, called monsoons, were cited as proving that 

 when the sun crossed the line or equator, its influence was exerted on 

 the wind, shifting its prevailing direction for a time either northwards 

 or southwards ; The ascent of the wann air over the heated plains of 



