42 TraiiHactions, — Miscellaneous. 



reciprocating the movements of the curves upon either side of it, and every 

 advantage must be taken of river-channels, mountain-passes, and other 

 such routes by which the contours can be shown to make their way across 

 the country ; the state of the sea, especially at exposed places, must also 

 be carefully shown by these contours ; and by close attention to these 

 principles, the occurrence of gales at points far distant from each other, 

 and the existence of but moderate winds at places close to where such gales 

 exist, can be accounted for, and reason can be shown why the sea- 

 disturbance is subject to similar irregularities, all apparently the effect 

 of purely local causes working independently of each other, but which are 

 in reality part of one system, whose effect is intensified at these points. 



The isobaric contour also enables another difficulty to be accounted 

 for; viz., the fact that the barometer moves more rapidly at some places 

 than it does at others ; and why, after it has fallen from a high point at 

 all stations, there are frequent instances of its not recovering its original 

 position over a considerable extent of country for a long time ; for instance, 

 let it be assumed that pressure ranges between 30*50 in the northern part 

 of this colony, and 30-20 in the south, and that a fall takes place amounting 

 to about seven-tenths of an inch in the latter, and two-tenths in the former 

 districts ; now, when a recovery sets in it will be found that the barometer 

 seldom rises to its original position at all places by a difference not unusually 

 amounting to half an inch at the southern stations, and although rapid 

 oscillations may take place in that part of the colony, yet pressure south- 

 ward of Napier does not return to its original position for a period varying 

 from a few days to several weeks. 



This general position of the lower pressure toward the south is in 

 accordance with our meteorological knowledge of this hemisphere, but it 

 does not seem to offer an explanation of why high readings of the barometer 

 in the south are not so unusual as may generally be supposed, and it should 

 render forecast easy, as it gives a gradient showing westerly winds ; but 

 experience in storm-warning shows that easterly winds are fi-equent, and 

 easterly gales must by no means be left out of the estimate of probable 

 weather, especially at places lying south of the 40th degree of latitude, as 

 it almost invariably hapj)ens that whenever the wind backs at places south- 

 ward of Napier it changes into north-east, although it does not always blow 

 a gale from that quarter. 



In the attempt to account for some of these points the isobaric contours 

 were of great value, and then use led to the idea of the possibility of the exis- 

 tence of multiple areas lying southward of contours, or lines of higher pressure, 

 which retreat or move northwards as the low areas approach ; advancing south- 

 wards when they have passed, or if they are passing at a considerable distance 



