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 wherein 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 are 
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 dow^n 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- 
