18 



ON THE SEPARATE PKESSURES OF THE AQUEOUS AND 



south, as is shewn by the general direction of the wind in those 

 parts. This abundance of condensation of vapour must heat 

 the air in the vicinity of Cape Horn up to a considerable 

 elevation, and render a thick stratum of it light, thus 

 accounting for the very low barometer observed there by 

 Captain Foster. The neighbourhood of Victoria land, as 

 ascertained by Captain Ross, presents the same general features 

 as Cape Horn, allowing for the greater proximity of the former 

 to the pole. The general gloom of the sky in this part, — the 

 frequent falls of rain and snow, and the low barometer, — all 

 indicate the presence of an atmosphere highly charged with 

 vapour in proportion to the temperature at the surface, which 

 atmosphere we presume must be drawn from warmer latitudes 

 towards the part by condensation. There being then an 

 abundance of aqueous matter in the air to furnish its full 

 proportion of weight, the low barometric pressure that is 

 found in these localities is evidently caused by the warming 

 and lightening of the gases, but the aqueous matter is not all 

 in the form of vapour. The particles of water that cause the 

 thick and gloomy mist have their proportion of the weight, 

 though it may be sustained by the gases in which they float, — 

 that weight however must be counteracted by the lightening 

 of the gases themselves, to produce the low aggregate'pressure 

 that is shewn by the barometer to exist there. 



From such evidence as can be obtained on the subject, we 

 thus arrive at the conclusion, that in every part of the world, 

 where there is a high average barometer, it is due to the gases 

 in the part, up to a considerable height, having fully acquired 

 the low temperature due to their elevation, — as then a greater 

 weight of air exists in the same space than when the gases 

 are locally warmed ; — whilst where the barometer is low, it is 

 always a consequence of heat having been conveyed by 

 vapour to warm the gases. This view also enables us to 

 account for the puzzling fact so long observed, of a moist 

 atmosphere being accompanied by a low, and a dry one by a 



