THE SPECIFIC GRAVITY OF THE SKi, ETC. ' 223 



water, let us fancy the southern hemisphere to have the land of the 

 northern, and the northern to have the water of the southern, the 

 earth's orbit remaining the same. Is it not obvious to our reason 

 that by this change the whole system of climatology in both hemi- 

 spheres would be changed ? The climates of our planet are as obe- 

 dient to law as the hosts of heaven. They are as they were 

 designed to be; and all those agents w^hich are concerned in 

 regidating, controlling, and sustaining them are "ministers of His." 

 Johnston, in the chapter to Plate XYIII. of his great Physical 

 Atlas, thus alludes to the seas, land, and climates of the two hemi- 

 spheres : " The mild winter of the southern hemisphere, plus the 

 contemporaneous hot summer of the northern hemisphere, neces- 

 sarily gives a higher sum of temperatm^e than the cool summer of 

 the southern, plus the cold winter of the northern hemisphere. 

 The above described relations appear to furnish the motive power in 

 the machinery of the general atmosphere of the earth in the periodi- 

 cal conversion of the aqueous vapours into liquid form. In this 

 manner the circuit of the fluid element, the essential support of all 

 vegetable and animal life, no longer appears to depend on mere 

 local coolings, or on the intermixtm^e of atmospheric currents of 

 different temperatui'es ; but the unequal distribution of land and 

 sea ui the northern and southern hemispheres supplies an effectual 

 provision, from whence it necessarily follows that the aqueous 

 vapour, which f^'om the autumnal to the vernal equinox is deve- 

 loped to an immense extent over the southern hemisphere, retui'ns 

 to the earth, in the other half of the year, in the form of rain or 

 snow\ And. thus the wonderful march of the most powerful steam- 

 enguie with which we are acquainted, the atmosj)here, appears to 

 be permanently regulated. The irregular distribution of physical 

 qualities over the earth's surface is here seen to be a preserving 

 principle for terrestrial life. Professor Dove considers the north- 

 ern hemisphere as the condenser in this great steam-engine, and 

 the southern hemisphere as its water reservoir ; that the quantity 

 of rain which falls ui the northern hemisphere, is, therefore, consi- 

 derably gi'eater than that which falls in the southern hemisphere ; 

 and that one reason of the high temperatm-e of the northern hemi- 

 sphere is that the larger quantity of heat which becomes latent in 

 the southern hemisphere in the formation of aqueous vapour is set 

 free in the north in great falls of rain and snow." 



456. In this view of what our little hydrometer has developed 

 or suggested, we trace the principles of compensation and adjust- 



