THE EQUATORIAL CLOUD-RING. 215 



ing on in the equatorial belt of precipitation, and this insight is 

 sufficient to enable us to perceive that exquisite indeed are the ar- 

 rangements which Nature has provided for supplying this calm 

 belt with heat, and for pushing the snow-line there high up above 

 the clouds, in order that the atmosphere may have room to ex- 

 pand, to rise up, overflow, and course back into its channels of 

 healthful circulation. As the vapor is condensed and formed into 

 drops of rain, a twofold object is accomplished : coming from the 

 cooler regions of the clouds, the rain-drops are cooler than the air 

 and earth below; they descend, and by absorption take up the heat 

 which has been accumulating in the earth's crust during the dry 

 season, and which can not now escape by radiation. Thus this 

 cloud-ring modifies the climate of all places beneath it ; overshad- 

 owing, at different seasons, all parallels from 5° south to 15° north, 



597. 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 with 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, north or south, is 

 regulated according to the seasons. 



598. If we imagine the atmospherical equator to be always 

 where the calm belt is which 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, 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 near- 

 ly the same temperature all the year round ; and so, too, would a 

 barometer the same pressure. 



