84 PHYSICAL GEOGRAPHY OF THE SEA, AND ITS METEaROLOGY. 



with an evaporating surface all the time. Aqueous vapour is very" 

 much lighter than atmospheric air : as this vapour rises, it becomes 

 entangled with the particles of air, some of which it carries up with 

 it, thus producing, through the liorizontal flow of air with tho 

 winds, numerous little ascending columns. As these columns of 

 air and vapour go up, the superincumbent j^ressm-e decreases, the 

 air expands and cools, causing precipitation or condensation of the 

 vapour. The heat that is set free dming this process expands the 

 air still fm-ther, thus causing here and there in those regions, and 

 wherever it may chance to be raining, intumescences, so to speak, 

 from the wind stratum below ; the upper current, sweeping over 

 these protuberances, bears them off in its course towards the 

 equator, and thus we have another turning back, and a constant 

 mingling. The curved arrows, h j h and Ji f Jc, are intended, on 

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

 up from the counter trades and turnmg back with the upper 

 current. 



229. Let us imagine the air to be visible, that we could see these 

 Supposing the air different strata of winds, and the air as it is sloughed 

 SI' would ITprr.'' off from one stratum to join the other. We can only 

 sented between the \[^QYi the spectaclo that would be presented between 



upper and lower cur- -^1-11 l j. ^ i? li • J i. 



rents. the uppor and the lower stratum oi these wmds to 



the combing of a succession of long waves as they come rolhng 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 up its 

 waters so as to keep them all alike. 



230. If the ordinances of natm-e requu'e a constant circulation 

 The importance of and coutinual mixiug up of the water in the sea^ 

 StioT^"^"*^^ ^'^'^'^' that it become not stagnant, and that it may be kept 

 in a wholesome state for its inhabitants, and subserve properly the 

 various offices requfred 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 ; stagnation 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 cir- 

 culation and intermingling of its ingredients are required of it. 

 Personal experience teaches us this, as is manifest in the recognized 

 necessity of ventilation in oiu" 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 



