THE EQUATORIAL CLOUD-RING. I79 



lire is diminished. These are physical laws, and therefore, when 

 we see water dripping from the atmosphere, we need no instru- 

 ment to tell us that the elasticity of the vapor so condensed, and 

 falling in drops, is less than was its elasticity when it was taken 

 up from the surface of the ocean as water, and went up mto the 

 clouds as vapor. 



362. Hence wti infer that, when the vapors of sea water are 

 condensed, the heat which was necessary to sustam them m the 

 vapor state, and which was borrowed from the ocean, is parted 

 with, and that therefore they were subjected, in the act of con- 

 densation, to a lower temperature than they w^ere in the act of 

 evaporation. Ceaseless precipitation goes on under this cloud- 

 ring. Evaporation under it is suspended almost entirely. We 

 know that the trade-winds encircle the earth ; that they blow per- 

 petually ; that they come from the north and the south, and meet 

 each other near the equator ; therefore we infer that this line of 

 meeting extends around the world. By the rainy seasons of the 

 torrid zone we can trace the declination of this cloud-ring stretch- 

 ed like a girdle round about the earth : it travels up and down the 

 ocean as from north to south and back. 



363. It is broader than the belt of calms out of which it rises. 

 As the air, with its vapors, rises up in this calm belt and ascends, 

 these vapors are condensed into clouds (§ 361), and this condensa- 

 tion is followed by a turgid intumescence, which causes the clouds 

 to -overflow the calm belt, as it were, both to the north and the 

 south. The air flowing off in the same direction assumes the 

 character of winds that form the upper currents that are counter 

 (Plate I.) to the trade-winds. These currents carry the clouds 

 still farther to the north and south, and thus make the cloud-ring 

 broader. At least, we infer such to be the case, for the rains are 

 found to extend out into the trade-winds, and often to a consider- 

 able distance both to the north and the south of the calm belt. 



364. Were this cloud-ring luminous, and could it be seen by an 

 observer from one of the planets, it would present to him an ap- 

 pearance not unhke the rings of Saturn do to us. Such an ob- 

 server would remark that this cloud-ring of the earth has a motion 

 contrary to that of the axis of our planet itself — that while the 

 earth was revolving rapidly from w^est to east, he would observe 

 the cloud-ring to go slowly, but only relatively, from east to west. 

 As the winds which bring the cloud-vapor to this region of calms 



