88 PHYSICAL CEOGllAniY OF THE SEA, AND ITS METEOKOLOGY. 



and tlius wo liavc another turning back, and a constant mingling. 

 Tho curved arrows, 1i j h and h' f h', are intended, on the 

 "diagram of the winds" (Plate I.), to represent this rising up 

 from the counter trades and turning back with the upper 

 current. 



229. Supposing the air visible, the spectacle that loould he presented 

 between the upper and lower currents. — Let ns imagine the air to be 

 visible, that we could see these different strata of winds, and the 

 air as it is sloughed off from one stratum to join the other. We 

 can only liken the spectacle that would be presented between 

 the upper and the lower stratum of these winds to the combing 

 of a succession of long waves as they come rolling in from the 

 sea, and breaking one after another, upon the beach. They curl 

 over and are caught up, leaving foam from their white caps 

 behind, but nevertheless stirring up the sea and mixing np its 

 waters so as to keep them all alike. 



230. The importance of atmospherical circulation. — If the ordi- 

 nances of nature require a constant circulation and continual 

 mixing up of the water in the sea, that it become not stagnant, 

 and that it may be kept in a wholesome state for its inhabitants, 

 and subserve properly the various offices required of it in the 

 terrestrial economy, how much more imperative must they not be 

 with the air ? It is more liable to corruption than water ; stag- 

 nation is ruinous to it. It is both the sewer and the laboratory 

 for the whole animal and vegetable kingdoms. Ceaseless motion 

 has been given to it ; perpetual circulation and intermingling of 

 its ingredients are required of it. Personal experience teaches 

 ns this, as is manifest in the recognized necessity of ventilation 

 in our buildings — the wholesome influences of fresh air, and the 

 noxious qualities of " an atmosphere that has in circulation." 

 Hence, continual mixing up of particles in the atmosphere being 

 required of the winds in their circuits, is it possible for the 

 human mind to conceive of the appointment of " circuits " for 

 them (§ 216) which are so admirably designed and exqui- 

 sitely adapted to the purpose as are those which this view 

 suggests ? 



231. Its vertical movements — how produced. — As a physical ne- 

 cessity, the vertical circulation of the air seems to be no less 

 important than its horizontal movements, which we call wind. 

 One begets the other. The wind, when it blows across parallels 

 of latitude — as it alwa3"s must, except at the equator, for it blows 



