THE EQUATORIAL CLOUD-RING. I77 



B56. In the process of condensation, these rain-drops, on the 

 other hand, have set free a vast quantity of latent heat, which has 

 been gathered up vrith the vapor from the sea by the trade-winds 

 and brought hither. The caloric thus liberated is taken by the 

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

 from the earth, the line of perpetual congelation. Were it possi- 

 ble to trace a thermal curve in the upper regions of the air to rep- 

 resent this line, we should no doubt find it mounting sometimes at 

 the equator, sometimes on this side, and sometimes on that of it, 

 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 is regulated accord- 

 ing to the seasons. 



357. If w^e imagine the atmospherical equator to be always 

 where the calm belt is w^hich separates the northeast from the 

 southeast trade-winds, then the loop in the thermal curve, which 

 should represent the line of perpetual congelation in the air, w^ould 

 be alw^ays 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 temperature all the year round ; and so, too, would a 

 barometer the same pressure. 



358. Its Office. — Returning and taking up the train of contem- 

 plation as to the office which this belt of clouds, as it encircles 

 the earth, performs in the system of oceanic adaptations, we may 

 Sep how the cloud-ring and calm zone which it overshadows per- 

 form the office both of ventricle and auricle in the immense atmos- 

 pherical heart, w^here 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. 



359. 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 ; and send out for distribu- 

 tion to the four corners, vapors 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 a well-constructed chro- 



M 



