178 THE PHYSICAL GEOGRAPHY OF THE SEA. 



nometer,. this cloud-ring affords the grand atmospherical machine 

 the most exquisitely arranged self -compensation. If the sun fail 

 in his supply of heat to this region^ more of its vapors are con- 

 densed, and heat is discharged from its latent store-houses in quan- 

 tities just sufficient to keep the machine in the most perfect com- 

 pensation. If, on the other hand, too much heat be found to ac- 

 company the rays of the sun as they impinge upon the upper cir- 

 cumference of this belt, then again on that side are the means of 

 self-compensation ready at hand ; so much of the cloud-surface 

 as may be requisite is then resolved into invisible vapor — for of in- 

 visible vapor are made the vessels v^^herein the surplus heat from 

 the sun is stored away and held in the latent state until it is call- 

 ed for, when instantly it is set free, and becomes an obvious and 

 active agent in the grand design. 



360. That the thermometer stands invariably lower (§ 351) be- 

 neath this cloud-belt than it does on either side of it, has not, so 

 far as my researches are concerned, been made to appear by ac- 

 tual observation, for the observations in my possession have not 

 yet been fully discussed concerning the temperature of the air. 

 But that the temperature of the air at the surface under this cloud- 

 ring is lower, is a theoretical deduction as susceptible of demon- 

 stration as is the rotation of the earth on its axis. Indeed, Nature 

 herself has hung a thermometer under this cloud-belt that is more 

 perfect than any that man can construct, and its indications 5te 

 not to be mistaken. 



361. Where do the vapors which form this cloud-ring, and 

 which are here condensed and poured down into the sea as rain, 

 come from? They come from the trade-wind regions (§ 115); 

 under the cloud-ring they rise up ; as they rise up, they expand ; 

 and as they expand, they grow cool, form clouds, and then are con- 

 densed into rains ; moreover, it requires no mercurial instrument 

 of human device to satisfy us that the air which brings the vapor 

 for these clouds can not take it up and let it down at the same 

 temperature. Precipitation and evaporation are the converse of 

 each other ; and the same air can not precipitate and evaporate, 

 take up and let down water, at one and the same temperature. 

 As the temperature of the air is raised, its capacity for receiving 

 and retaining water in the state of vapor is increased ; as the tem- 

 perature of the air is lessened, its capacity for retaining that moist- 



