SEA ROUTES, CALM BELTS, AND VARIABLE WINDS. 357 



and, of course, the sailor in command most of all ; indeed, a sea 

 voyage more than fulfils my expectations." 



G65. Winds blow from a high to a loio barometer. — It appears, 

 therefore, that the low barometer about the poles and the low 

 barometer of the equator cause an inrush of wind, and in each 

 case the rushing wind comes from the high and blows towards the 

 low barometer ; that in one hemisphere the calm belt of Capri- 

 corn, and in the other the calm belt of Cancer, occupies the 

 medial line between the equatorial and polar places of low 

 barometer. 



660. Polar rarefaction. — It appears, moreover, that the polar 

 refraction is greater than the equatorial, for the mean height of 

 the austral barometer is very much below that of the equatorial, 

 and, consequently, its influence in creating an indraught is felt 

 at a greater distance (Plate XV.) — even at the distance of 50° of 

 latitude from the south pole, while the influence of the equatorial 

 depression is felt only at the distance of 30° in the southern, and 

 of 25° in the northern hemisphere. The diff*erence as to degree 

 of rarefaction is even greater than this statement implies, for the 

 influx into the equatorial calm belt is assisted also by tempera- 

 ture in this, that the trade- winds blow from cooler to warmer 

 latitudes. The reverse is the case with the counter-trades ; 

 therefore, while difterence of thermal dilatation assists the equa- 

 torial, it opposes the polar influx. 



667. The tropical calm belts caused by the polar and equatorial 

 calms. — Thus we perceive that the tropical calm belts are simply 

 an adjustment between the polar and equatorial calms; that the 

 tropical calm belts assume their position and change their lati- 

 tude in obedience to the energy with which the influence of the 

 heated and the expanding columns of air, as they ascend in the 

 polar and equatorial calms, is impressed upon them. 



668. TJie meteorological power of latent heat. — This explanation of 

 the calm places and of the movements of the low austral ba- 

 rometer shows, comparatively speaking, how much the latent 

 heat of vapour, and how little the direct heat of the sun has to 

 do in causing the air to rise up and flow off from these calm 

 places, and consequently, how little the direct action of the solar 

 ray has to do either with the trades or the counter trades. It 

 regulates and controls them ; it can scarcely be said to create 

 them. 



669. The low barometer off Cape [Horn. — The fact of a low 



