﻿and Fluctuations. 343 



feeble that the withdrawal of even the whole of it could not pro- 

 duce any marked effect. But northerly winds are themselves 

 rare, winds from the south, from the east, or from the west 

 alternating irregularly south of the parallel of 65°; and. it must 

 be remembered that the immense snow fields are the accumula- 

 tions of years, perhaps of centuries, and that the actual increase 

 each year is probably small. 



It has often been suggested that the centrifugal tendency due 

 to the rotation of the earth may possibly be the cause of this 

 singular depression of the barometer; but the suggestion has 

 met with but little favour, because, if the centrifugal tendency 

 occasioned a low barometer in the neighbourhood of the south 

 pole, it might fairly be expected to occasion it also near the 

 north pole, and it has been very positively said that in this last- 

 named region the barometer is not low. This statement is in- 

 correct. In most places within the Arctic circle where we have 

 observations, the barometer does stand very low ; and although 

 the depression does not seem to be either so great or so regular 

 as in the Antarctic, it is none the less a very well-established fact. 

 I have therefore no hesitation in agreeing in great measure with 

 those who would refer it to a centrifugal tendency, believing 

 that the irregularities which occur in both regions, but more 

 especially in the Arctic, are in most instances capable of satisfac- 

 tory explanation. 



The attempt to calculate accurately the amount of depression 

 at the poles which this centrifugal tendency should occasion 

 seems at present quite hopeless; the results which have been 

 obtained have, for want of satisfactory data, been so utterly erro- 

 neous that they have no value whatever. But leaving abstract 

 science on one side^ and being guided by observation only, it 

 would appear that the depression which can be attributed to the 

 centrifugal tendency does not exceed, and is perhaps rather less 

 than one inch ; for though there is reason to believe that the 

 extreme depression is considerably more, we cannot overlook the 

 fact that there are other forces in operation which must modify 

 and in some instances increase the effect due to the rotation of 

 the earth. Of these forces, one of the most important is that 

 called into action by the winds which prevail in the southern 

 hemisphere north of the antarctic circle. From the parallel of 

 60° northwards to the parallel of 40° these winds blow almost 

 constantly from the west ; they are not, as has been frequently 

 said, north-west winds ; neither are they south-west ; but though 

 found occasionally, or in some special locality generally, inclined 

 the one way or the other, their prevailing direction right round 

 the world is due west. These winds have a strength far beyond 

 that of any other prevailing winds on the face of the earth ; in 



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