THE CLOUD REGION, ETC. 281 



excess of precipitation. 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 ceaseless volumes of heated air, which, loaded to 

 saturation with vapour, has to rise above and get clear of the 

 clouds before it can commence the process of cooling by radia- 

 tion. In the mean time, also, the vapours which the trade- 

 winds bring from the north and the south, expanding and 

 growing cooler as they ascend, are being condensed on the lower 

 side of the cloud stratum, and their latent heat is set free, to 

 check precipitation and prevent a flood. While this process and 

 these operations are going on upon the nether side of the cloud- 

 ring, one not less important is, we may imagine, going on upon 

 the u]_3per side. There, from sunrise to sunset, the rays of the 

 sun are pouring down without intermission. Every day, and all 

 day long, they play with ceaseless activity upon the upper 

 surface of the cloud stratum. When they become too powerful, 

 and convey more heat to the cloud vapours than the cloud 

 vapours can reflect and give off to the air above them, then, with 

 a beautiful 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. We thus have an 

 insight into the operations which are going on in the equatorial 

 belt of precipitation, and this insight is sufficient to enable us to 

 perceive that exquisite indeed are the arrangements which 

 Nature has provided for supplying this calm belt with heat, 

 and of pushing the snow-line there high uip above the clouds, in 

 order that the atmosphere may have room to expand, to rise up, 

 overflow, and course back into its channels of healthful circula- 

 tion. As the vapour is condensed and formed into drops of rain, 

 a two-fold 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 cannot now esca23e by radiation. 



520. Snow-line mounts up as it crosses the equatorial calm belL — 

 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 vapour fiom the sea b}^ the trade-winds and 

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



