The Low Barometer of the Antarctic Temperate Zone. 343 



relation of cause and effect. In fact, in New Holland, where 

 hot winds bring dry air, we find the barometer low when the 

 air is dry. 



It follows from what has just been said of the manner in 

 which aqueous vapour associates itself with air, that atmo- 

 spheric pressure is increased instead of diminished by the 

 process of quiet evaporation, since the weight of the vapour is 

 added to that of the air. Therefore, all things being equal, we 

 should expect to find the barometer higher in the southern or 

 watery hemisphere than in the northern. 



It might seem unnecessary to consider Maury's theory* 

 further, but as some doubts may still remain whether some 

 process of the kind conceived by him may not take place,* I 

 proceed to consider the efficiency of such a process to account 

 for the great phenomenon we are dealing with. 



It must be remembered, in the first place, that the theory 

 requires that there should be a greater volume of mixed air 

 and vapour over the southern temperate zone, than there is in 

 the corresponding northern zone, otherwise there would not be 

 that continual overflow towards the equator which is required 

 by the theory. So far as it goes, this increment of volume 

 implies an increment of weight. The increase of volume is 

 more than compensated (in theory) by diminution of specific 

 gravity, but it must be held in mind that the increase of 

 volume has to be accounted for by the theory as well as the 

 difference in barometric pressure. 



Again, the theory requires that the upper regions of air 

 should be dry, for it is the upper air that is carried towards the 

 equator ; and if this air were moist, we should no longer have 

 the different proportions of moist and dry air which are 

 required by the theory. We must have an aggregation of 

 moist air in high southern latitudes, and of dry air towards the 

 equator. 



Again, we must call to mind that one- half of the northern 

 hemisphere is covered by water, and a part of the southern 

 hemisphere is not so covered, so that the effects suggested by 

 Maury are (1) not peculiar to the southern hemisphere, nor (2) 

 do they prevail over the whole of that hemisphere. 



Lastly, we must remember that the process conceived by 

 Maury must be wholly or principally a diurnal process, and so 



* In fact, Sir. J. Herschel, in his work on Meteorology, assigns as a cause of 

 the low barometric pressure near the equator, compared with that near the tropics, 

 a process similar to that conceived by Maury, only depending on the excess of 

 heat near the equator. I cannot but agree with those meteorologists who consider 

 that the notion of any appreciable uplifting of the air by the rising vapour of 

 water is a mistaken one. But whether it be so or not, it is evident that Herschel's 

 view would require a regular increase of pressure from the equator to the 

 antarctic pole, and therefore is opposed to Maury's explanation. 



