14' 



CHAPTEE YII. 



§ 341-368. — THE EASTING OF THE TKADE-WIXDS, THE CROSSIKa 

 AT THE CALM BELTS, AND THE MAGInETISM OF THE ATMOSPHERE. 



341. Halley's theory of the trade-winds, especially so mncli of it 

 iiaiiey'sdieorynot as ascribcs their castcrly direction to the effect of the 

 observSns!^ '^ diumal rotation of the earth, seems to have been 

 generally received as entirely correct. But it is only now, since 

 all the maritime nations of the world have nnited in a common system 

 of research concerning the physics of the sea, and occupied it with 

 observers, that we have been enabled to apply the exioerimentum 

 crucis to this part of the famous theory. The abstract logs, as the 

 observing-books are called, have placed within my reach no less 

 than 632,460 observations — each one itself being the mean of 

 many separate ones — upon the force and direction of the trade- 

 winds. It appears from these that dim^nal rotation being re- 

 garded as the sole cause, does not entirely account for the easting 

 of these winds. 



342. From these observations the following table has been com- 

 observed course of piled. It shows the mcau annual direction of the 

 the trade-wiuds. tradc-wuids in each of the six belts, north and south, 

 between the parallels of 30° and the equator, together with the 

 number of observations from which the mean for the belt is derived : 



Between 



30^ and 25° 

 25° and 20° 

 20° and 15° 

 15° and 10^ 

 10° and 5° 

 5° and 0° 



Mean . . . 



N.E. Trades. 



Course. 



No. of Obs. 



N. 



51° 



51° 30' 

 53° 30' 

 52° 30' 

 53° 30' 

 54° 30' 



E. 



N. 52° 45' E. 



G8, 777 

 44, 527 

 33, 103 

 30, 339 

 36, 841 

 67, 829 



S.E. Trades. 



Course. 



S. 46° 

 49° 20' 

 52° 



49° 40' 

 51° 40' 

 48° 40' 



S. 49° 33' E. 



No. of Obs. 



66, 635 

 66, 395 

 46, G04 

 43, 817 

 54, 648 

 72.945 



Between the equator and 5° north, the annual average dm-ation of 

 the trades is 67 days for the north-east, and 199 for the south-east, 



L 2 



