§ 811-813. THE WINDS OF THE SOUTHERN HEMISPHERE. 433 



CHAPTER XX. 



§ 811-8^1. — THE WINDS OF THE SOUTHERN HEMISPHERE. 



811. A WORK of this sort, which is progressive, must necessari- 

 Repetition often neces- ^J t)ear with it more or less of repetition. It em- 

 ^''"^'' bodies the results of the most extensive system of 

 philosophical observations, physical investigation, and friendly co- 

 operation that has ever been set on foot. As facts are developed, 

 theories are invented or expanded to reconcile them. As soon as 

 this is done, or in a short time thereafter, some one or more of the 

 fleets that are out reconnoitring the seas for us returns with addi- 

 tional facts for our store-house of knowledge. Whether these tend 

 to confirm or disprove the theory, a restatement is often called for ; 

 hence the repetition, of which the case before us is an example. 



812. The facts stated in Chap. XY. go to show that the south- 

 The S.E. and N.E. east tradc-wiuds are stronger than the northeast. 



tnide-winds put in a *-' 



balance. Thc baromctcr tells us (§ 613) that between the 



parallels of 5° and 20° the southeast trade-winds bear a super- 

 incumbent pressure upon the square foot of nearly 4 pounds 

 greater than that to which the northeast trades are subjected. 

 Such an excess of superincumbent pressure ujDon a fluid so elastic 

 and subtle as air ought to force the southeast trade-winds from 

 under it more rapidly than the lighter pressure forces the north- 

 cast. Observations showing that such is or is not the case should 

 not be ignored. 



813. I have evidence from all the vessels in a fleet numbering 

 Observations by 2235 ^^^ Icss than 2235 Sail to show that the southeast 

 '''''''■'^^■'' are stronger than the northeast trades. Every one 

 of these vessels passed through both systems of trade-winds. The 

 knots run per hour by each one of them, as they passed through 

 the southeast trades of the Indian Ocean and through both sys- 

 tems of the Atlantic, have been discussed from crossing to cross- 

 ing. The average result in knots per hour is expressed in the an- 

 nexed table, p. 434. The comparison is confined to the rate of 

 sailing between the parallels of 10° and 25°, because this is the 

 belt of steadiest trades. 



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