230 THE PHYSICAL GEOGRAPHY OF THE SEA. 



oar reason that by this change the whole system of climatology 

 in both hemispheres would be changed ? The climates of our 

 planet are as obedient to law as the hosts of heaven. They are 

 as they were designed to be ; and all those agents which are con- 

 cerned in regulating, controlling, and sustaining them are " minis- 

 ters 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 hemispheres : " The mild winter of the southern hemisphere, 

 plus the contemporaneous hot summer of the northern hemi- 

 sphere, necessarily gives a higher sum of temperature 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 periodical conversion of the aqueous vapors into 

 liquid form. In this manner the circuit of the fluid element, the 

 essential support of all vegetable and animal life, no longer ap- 

 pears to depend on mere local coolings, or on the intermixture of 

 atmospheric currents of different temperatures ; but the unequal 

 distribution of land and sea in the northern and southern hemi- 

 spheres supplies an effectual provision, from whence it necessarily 

 follows that the aqueous vapor, which from the autumnal to the 

 vernal equinox is developed to an immense extent over the south- 

 ern hemisphere, returns 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-engine with which we are acquainted, 

 the atmosphere, appears to be permanently regulated. The irreg- 

 ular distribution of physical qualities over the earth's surface is 

 here seen to be a preserving principle for terrestrial life. Profess- 

 or Dove considers the northern hemisphere as the condenser in 

 this great steam-engine, and the southern hemisphere as its water 

 reservoir ; that the quantity of rain which falls in the northern 

 hemisphere is, therefore, considerably greater than that which 

 falls in the southern hemisphere ; and that one reason of the 

 higher temperature of the northern hemisphere is that the larger 

 quantity of heat which becomes latent in the southern hemisphere 

 in the formation of aqueous vapor 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- 



