41 G PHYSICAL GEOGRAPHY OF THE SEA, AND ITS METEOROLOGY. 



CHAPTEE XX. 



§ 811-842. THE WINDS OF THE SOUTHERN HEMISPHERE. 



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

 Repetition often ne- hear with it more or less of repetition. It em- 

 cessary. hodies 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 

 additional facts for our storehouse 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 ui Chap. XY. go to show that the south- 

 The S.E. and N.E. gast tradc-'svinds are stronger than the north-east, 

 a batauce. " ^"* ^"^ The baromctcr tells us (§ 643) that between the 

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

 incumbent pressure upon the square foot of nearly 4 pounds greater 

 than that to which the north-east trades are subjected. Such an 

 excess of superincumbent pressure upon a fluid so elastic and 

 subtle as ah', ought to force the south-east trade-winds from under 

 it more rapidly than the hghter pressure forces the north-east. 

 Observations showing that such is or is not the case should not be 

 ignored. 



813. I have the separate and independent e\ddence from every 

 Observations by 2235 vcsscl in a fleet numbering no less than 2235 sail to 

 vessels. qJiqw that the S.E. are stronger than the N.E. trades. 

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

 The Imots run per horn* by each one of them, as they passed through 

 the south-east trades of the Indian Ocean and through both systems 

 of the Atlantic, have been measured and discussed from crossing to 

 crossing. The average result in knots is expressed in the annexed 

 table, P. 417. The comparison is confined to the rate of sailing 

 between the parallels of 10° and 25°. because this is the^belt of 

 steadiest trades. 



