﻿330 Mr. J. K. Laughton on Barometric Differences 



the average, nearly an inch lower than in other parts of the 

 world. But over an area so vast as the Antarctic, and so cold 

 even in the summer months, the air must be contracted to an 

 extreme density ; and though the temperature is probably much 

 greater than that of Siberia or the eastern steppes of Asia during 

 the winter, it is still very far below that of any other portion of 

 the southern hemisphere ; so that if increase of density neces- 

 sarily led to a corresponding increase of elastic force, the observed 

 barometric pressure in the Antarctic would be markedly higher 

 than in any other part of the southern hemisphere, not lower. 



The more exact oar observations become, the greater and more 

 persistent is the difficulty which opposes the idea that cold in- 

 creases barometric pressure. Mr. Buchan, in his isobaric charts, 

 shows a large patch of high pressure during the winter in Eastern 

 Siberia, and at the same season a patch of low pressure in the 

 neighbourhood of Iceland. These differences he considers due 

 to the extreme cold of Siberia and the relative warmth of Iceland*. 

 But by what principle of selection, according to such a view, does 

 the barometer choose Iceland as its centre of minimum pressure ? 

 for the south-west corner of Ireland, at no very great distance, 

 has a very much higher average winter temperature than the 

 western side of Iceland ; and still further to the south-west, 

 towards the Azores, the temperature is still higher ; so that even 

 if, leaving other considerations momentarily on one side, we were 

 disposed partially to admit that the extreme long-continued and 

 unbroken cold of Siberia does permit an accumulation of air 

 there, and produce this remarkable increase of barometric pres- 

 sure through the winter, we cannot admit that the relative 

 warmth of Iceland (relative only to Siberia) can so reduce the 

 barometric pressure in that neighbourhood as to render it feeble 

 relatively to that of much warmer districts neither remote nor 

 separated by geographical barriers. 



Many other instances might be brought forward ; but those I 

 have mentioned afford sufficient proof that heat, even long con- 

 tinued over a wide area, does not necessarily establish a relatively 

 low barometer; nor does long-continued cold establish a high. 

 This is in conformity with our everyday experience on a small 

 scale ; for we know that the barometer is by no means necessarily 

 higher in cold weather than in hot, and that its mean height in 

 England is very much the same in winter as in summer. There 

 is, as I have shown, reason to believe that a rise of temperature 

 does in some instances affect the barometer and cause an alter- 

 nation of high and low pressure ; but there seems no support in 

 geographical fact for the opinion that continued high or low 

 temperature sensibly affects the barometric mean of the district 

 subjected to it. 



* Handy Book of Meteorology, p. 40. 



