176 
THE PHYSICAL GEOGRAPHY OF THE SEA. 
is thus interrupted, and the excess of heat in the earth is dehvered 
to the air, and by absorption carried up to the clouds, and there 
transferred to their vapors to prevent excess of precipitation, 
353. In the mean time, the trade-winds north and south are 
pouring into this cloud-covered receiver, as the calm and rain-belt 
of the equator may be called, fresh supplies in the shape of cease- 
less volumes of heated air loaded to saturation with vapor, which 
has to rise above and get clear of the clouds before it can com- 
mence the process of cooling by radiation. In the mean time, 
also, the vapors which the trade-winds bring from the north and 
the south, expanding and growing cooler as they ascend, are be- 
ing condensed on the lower side of the cloud stratum, and their 
latent heat is set free, to check precipitation and prevent a flood. 
354. While this process and these operations are going on upon 
the nether side of the cloud-ring, one not less important is going 
on upon the upper side. There, from sunrise to sunset, the rays of 
the sun are pouring down without intermission. Every day, and 
all day long, they operate with ceaseless activity upon the upper 
surface of the cloud stratum. When they become too powerful, 
and convey more heat to the cloud vapors than the cloud vapors 
can reflect and give olF to the air above them, then, with a beau- 
tiful elasticity of character, the clouds absorb the surplus heat. 
They melt away, become invisible, and retain, in a latent and 
harmless state, until it is wanted at some other place and on some 
other occasion, the heat thus imparted. 
355. We thus have an insight into the operations which are go- 
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. 
