EQUATORIAL CALMS AND WINDS. 153 



the air which is brought to the Equator by the N.E. and S.E. Trades 

 ascends. This Belt of Calms always separates these two Trade Wind 

 zones, and travels up and down with them. If we liken this Belt of 

 Equatorial Calms to an immense atmospherical trough, extending as it 

 does entirely around the earth; and if we liken the N.E. and S.E. Trade 

 Winds to two streams discharging themselves into it, we shall see that we 

 have two currents perpetually running in at the bottom, and that, there- 

 fore, we must have as much air as the two currents bring in at the bottom 

 to flow out of the top. What flows out of the top is carried back North 

 and South by the upper currents (8), which are thus proved to exist and 

 to flow counter to the Trade Winds." 



This Belt of Calms follows the sun in his annual course, though the 

 limits do not range so much in latitude as the sun does in declination ; 

 and, generally, they pass from one extreme of latitude to another in about 

 three months. The whole system of Wind and Calm Belts moves North- 

 ward from the latter part of May till some time in August ; it then remains 

 almost stationary till the approach of winter, when it commences to go 

 Southward, and proceeds in that direction from December to February or 

 March. 



"The great 'sun siving ' of this Calm Belt," says Captain Maury, " is 

 annual in its occurrence ; it marks the seasons, and divides the year into 

 wet and dry for all those places that are within the arc of its majestic sweep. 

 But there are other subordinate and minor influences which are continually 

 taking place in the atmosphere, and which are also calculated to alter the 

 place of this Calm Belt, and to produce changes in the thermal status of 

 the air which the Trade Winds move. These are unusually severe winters 

 or hot summers ; remarkable spells of weather, such as long continuous 

 rains or droughts, over areas of considerable extent. Either within or near 

 the Trade Wind belts it is tremblingly alive to all such influences, and they 

 keep it in continual agitation ; accordingly we find that such is its state, 

 that, within certain boundaries, it is continually changing place and limits. 

 This fact is abundantly proved by the speed of ships, whose log-books show 

 that it is by no means a rare occurrence for one vessel, after she has been 

 dallying in the Doldrums for days, in the vain effort to cross that Calm 

 Belt, to see another coming up to her 'hand over fist,' with fair winds, and 

 crossing the belt after a delay in it of only a few hours instead of days."* 



(76.) These remarks of Captain Maury, coupled with the experience of 

 most sailors who cross the Line, will demonstrate that the limits of this 

 Calm Belt cannot be very exactly defined, and it is only the doctrine of 

 chances that can determine when any particular ship will lose the Trades, 

 and encounter the Doldrums. 



On page 132 (54), is given the Table drawn up by Captain Hors burgh, 

 as the probable Equinoctial Limits of the N.E. and S.E. Trades, and con- 

 sequently of the intervening Belt of Calms. This apphes to that part of 

 them, between 18° and 26° W., which was usually traversed by the East 

 India Company's ships. The diagram of the Winds, and also the charts 



• " Physical Geography of the Sea," 1860, page 358. 



m. A. 0, 21 



