LOW BAROMETER OF ANTARCTIC ZONE. 295 



difference, lie writes: To explain the great and 

 grand phenomena of nature, by illustrations drawn from 

 the puny contrivances of human device, is often a feeble 

 resort, but nevertheless we may, in order to explain 

 this expulsion of air from the watery south, where all 

 is sea, be pardoned for the homely reference. We all 

 know, that, as the steam or vapour begins to form in 

 the tea-kettle, it expels air thence, and itself occupies 

 the space which the air occupied. If still more heat be 

 applied , as to the boiler of a steam-engine, the air will be 

 entirely expelled, and we have nothing but steam above 

 the water in the boiler. Now at the south over this 

 great waste of circumfluent waters, we do not have as 

 much heat for evaporation as in the boiler or the tea 

 kettle ; but, as far as it goes, it forms vapour, which 

 has proportionately precisely the same tendency that 

 the vapour in the tea-kettle has to drive off the air 

 above, and occupy the space it held. Nor is this all. 

 This austral vapour, rising up, is cooled and condensed. 

 Thus a vast amount of heat is liberated in the upper 

 regions, which goes to heat the air there, expand it, and 

 thus, by altering the level, causes it to flow off. 



The theory thus divides itself into two parts : we 

 have first the expulsive effects due to the vapour 

 raised from southern oceans ; and, secondly, the expan 

 sive effects due to the liberation of heat as the vapour 

 is condensed. Now I would, in the first place, submit 

 that we cannot assign to the second cause the effects 

 here considered. The amount of heat liberated as the 

 vapours rising from southern ocean are condensed is 



