80 PHYSICAL GEOGRAPHY OF THE SEA, AND ITS METEOROLOGY. 



but, Avere the explanation to rest here, a nortli-east trade-wind 

 extending from the polo to the equator would satisfy it; and 

 were this so, we should have, on the surface, no winds but the 

 north-east trade-winds on this side, and none but south-east 

 trade-winds on the other side, of the equator. 



209. From the Pole to 30°-35o. — Let ns return now to our 

 northern particle (§ 207), and follow it in a round from the 

 north pole across the equator to the south pole, and back again. 

 Setting off from the polar regions, this particle of air, for some 

 reason which does not appear, hitherto, to have been verj^ satis- 

 factorily explained by philosophers, instead of travelling (§ 208) 

 on the surface all the way from the pole to the equator, travels 

 in the upper regions of the atmosphere until it gets near the belt 

 between 30^-35°. Here it meets, also in the clouds, the hypo- 

 thetical particle that is coming from the south, and going north 

 to take its place. 



210. The ''horse latitudes y—kho\xi\h.\s belt of 30^-35° north, 

 then, these two particles press against each other with the whole 

 amount of their motive power, and produce a calm and an 

 accumulation of atmosphere : this accumulation is sufficient to 

 balance the pressure of the two currents from the north and 

 south. From under this bank of calms, which seamen call the 

 " horse latitudes," two surface currents of wind are ejected or 

 drawn out ; one towards the equator, as the north-east trades, 

 the other towards the pole, as the south-west "passage-winds," 

 or counter-trades. These winds come out at the lower surface 

 <ii the calm region, and consequently the place of the air borne 

 away in this manner must be supplied, we may infer, by do^vn- 

 ward currents from the superincumbent air of the calm region. 

 Like the case of a vessel of water which has two streams from 

 opposite directions running in at the top, and two of eqnal 

 •capacity discharging in opposite directions at the* bottom, the 

 motion of the water would be downward ; — so is the motion of 

 the air in this calm zone. 



211. Tlie harometer there. — The barometer, in this calm region, 

 •stands higher than it does either to the north or to the south of 

 it; and this is another proof as to the accumulation of the 

 .atmosphere here, and pressure from its downward motion. And 

 because the pressure under this calm belt is greater than it is 

 on either side of it, the tendency of the air will be to flow 

 out on either side ; therefore, supposing we were untaught by 



