282 PHYSICAL GEOGRAPHY OF THE SEA, AND ITS METEOBOLOGy. 



and carried up aloft still farther, to keep, at the proper distance 

 from the earth, the lino of perpetual congelation. Were it pos- 

 sible to trace a thermal curve in the upper regions of the air to 

 represent this line, we should no doubt find it mounting some- 

 times at the equator, sometimes on this side, and sometimes on 

 that, but always so mounting as to overleap this cloud-ring. This 

 thermal line would not ascend always over the same parallels : it 

 would ascend over those between which this ring happens to be ; 

 and the distance of this ring from the equator, north or south, is 

 regulated according to the seasons. If we imagine the atmo- 

 spherical equator to be always where the calm belt is which 

 separates the north-east from the south-east trade-winds, then the 

 loop in the thermal curve, which should represent the line of per- 

 petual congelation in the air, would be always found to stride 

 this equator ; and it may be supposed that a thermometer, kept 

 sliding on the surface of the earth, so as always to be in the 

 middle of this rain-belt, would show very nearly the same tempe- 

 rature all the year round ; and so, too, would a barometer the 

 same pressure, though the height of the atmosphere over this 

 calm belt would, in consequence of so much heat and expansion, 

 be very much greater than it is over the trade- winds or tropical 

 calms. 



521. Offices of the cloud-ring. — Returning and taking up the 

 train of contemplation as to the office which this belt of clouds, 

 as it encircles the earth, performs in the system of oceanic adapta- 

 tions, we may see how the cloud-ring and calm zone which it 

 overshadows perform the office both of ventricle and auricle in 

 the immense atmospherical heart, where the heat and the forces 

 which give vitality and power to the system are brought into 

 play — where dynamical strength is gathered, and an impulse 

 given to the air sufficient to send it thence through its long and 

 tortuous channels of circulation. 



522. It acts as a regulator. — Thus this ring, or band, or belt of 

 clouds is stretched around our planet to regulate the quantity of 

 precipitation in the rain-belt beneath it; to preserve the due 

 quantum of heat on the face of the earth ; to adjust the winds ; 

 und send out for distribution to the four corners vapours in 

 proper quantities to make up to each river-basin, climate, and 

 season its quota of sunshine, cloud, and moisture. Like the 

 balance-wheel of an artificial machine, this cloud-ring affords the 

 grand atmospherical machine the most exquisitely-arranged self- 



