TRADE-WINDS OF THE SOUTHERN HEMISPHERE. 



855 



Average Speed through the Trade-winds of the North and South 

 Atlantic Oceans. 



January 



February 



March 



April 



May 



June 



July 



August 



September 



October 



November 



December 



Means 



KNOTS PEE HOUR, FROM 



25° to 20°. 20° to 15°. 15° to 10' 



5i 6 Gi 



AVERAGE. COURSE STEERED THROUGH 



S.E. Trades. 



N. 54° W. 

 N. 55 W 

 N. 55 W, 

 N. 53 W, 

 N. 55 W. 

 N. 55 W 

 N. 55 W, 

 N. 55 W. 

 N. 55 W. 

 N. 5G W. 

 N. 55 W, 

 N. 55 W. 



7-k 

 7 



n 



7i 



7 



5 



4i 



4 



5 



4f 



5i 



It 



6 6 5f N. 55° W. S. 24° E 



N.E. Trades. 



S. 21° 

 S.25 

 S. 22^ 

 S. 22^ 

 S. 24J 

 S. 28 

 S.27 

 S. 28^ 

 S. 22i 

 S. 20 

 S.22i 

 S.23 



Average course steered through the S.E. trades, N.W. by W. 

 " " " N.E. trades, S.S.E. 



It is well to observe, tliat on eacli of these tliree oceans, tliougli 

 tlie direction of tlie wind is the same, the course steered by each 

 fleet is different ; consequently, these anemometers are at different 

 angles with the wind ; through the southeast trades the wind is 

 nearly aft in the Atlantic, and quartering in the Indian Ocean ; 

 giving an average sailing speed of 7 knots an hour in the former, 

 and of 6 in the latter; while through the northeast trades the 

 average speed is 6i knots an hour one way (JST.W. J W.), with 

 the wind just abaft the beam, and 5f the other (S.S.E.), with 

 the wind at a point not so favorable for speed. Indeed, most of 

 the ships which average a S.S.E. course through this part of the 

 northeast trade-wind belt are close hauled ; therefore the average 

 strength of the trades here can not be fairly compared with the 

 average strength where the fleet have free winds. What is the 

 difference in the strength of such winds, which, impinging upon 

 the sails, each at the particular angle indicated above, imparts the 

 aforesaid velocities ? Moderate winds, such as these are, give a 

 ship her highest speed generally when they are just abaft the 

 beam, as they are for a northwest course through the northeast 

 trades. So, to treat these shi|)s as anemometers that will really 

 enable us to measure the comparative strength of the winds, we 



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