338 The Low Barometer of the Antarctic Temperate Zone. 



20,000,000,000,000 tons greater than the atmospherical pres- 

 sure on the southern hemisphere. 



Such a peculiarity as this may almost deserve to be spoken 

 of in the terms applied by Sir J. Herschel to the distribution 

 of land and water upon our earth, it is li massive enough to 

 call for mention as an astronomical feature. 33 I propose to, 

 examine two theories which have been suggested in explana- 

 tion of this feature of the earth'' s envelope. These theories 

 are founded on local peculiarities, and the feature considered 

 appears as a dynamical one — that is, as a peculiarity resulting 

 from states of motion in the aerial envelope. I shall endeavour 

 to establish a theory founded on a consideration of the earth's 

 mass as a ivhole, and presenting the atmospheric feature in 

 question as a statical one. 



The first theory I have to notice is one founded on the 

 configuration of land and water upon the northern and 

 southern hemispheres of the earth's globe. In the northern 

 hemisphere, and more especially in that part of the northern 

 hemisphere in which barometrical observations have been most 

 persistently and systematically conducted, there is much more 

 land than in the southern hemisphere. Now barometrical 

 observations are referred to the sea-level, and observations 

 made in Europe and America may be considered as referred to 

 the level of the northern parts of the Atlantic Ocean. It is 

 argued that the North Atlantic, compared with southern 

 oceans, is little more than "a, large lake, having elevated 

 banks east and west." " Practically, the air there is a portion 

 of the solid globe, so that the unconfined air will rest upon 

 and rise above the former, as if it were solid and a portion of 

 the earth; so that the altitude of the air over the North 

 Atlantic will be increased some hundreds of feet, and the 

 barometer at the sea-level will be pressed upon, not only by 

 the free air clear of the earth's banks, but also by the air 

 confined in the basin, much as if the air were at the bottom of 

 a mine."* 



Presented in the above form, the theory that the higher 

 northern barometer is due to the contour of the northern 

 hemisphere scarcely deserves serious comment. To speak of the 

 confined air of the North Atlantic Ocean is surely unreasonable. 

 An ocean 2000 miles across, swept by more frequent t storms 

 than are experienced in any other part of the globe, cannot be 

 very aptly compared to " the bottom of a mine." An inelastic 

 fluid flowing steadily over a rugged surface shows no trace, or 

 but the slightest trace, of the nature of that surface by &ny 

 variations of its own level. But it is still less conceivable 



* From a letter addressed to the editor of the AtJienceum, by Dr. H. 

 Muirhead. 



