§ 343, 344. 



EASTING OF THE TRADE-WINDS, ETC. 



149 



ing winds between those parallels — of S.47° 80' E. According to 

 the Halleyan theory they should be southwest winds. 



343. In the Atlantic the average velocity of the southeast is 

 Velocities of the trade- grater than the average velocity of the northeast 

 '''^^'' trades.* I estimate one to be from 14 to 18, the 



other from about 25 to 30 miles an hour. Assuming their veloc- 

 ity to be 14 and 25, the following dej^artures show the miles of 

 easting which the trade-winds average per hour through each of 

 the above-named belts : 



Hourly Rate of Departure across the Trade-wind Belts. 



844. That diurnal rotation does impart easting to these winds 

 Difference between thcrc is no doubt ; but thc path suggcstcd by the 



observation and the- ^ ^ ^ „ , ^ • ^ t 



cry. table does not coniorm to that which, according to 



any reasonable hypothesis, the trade-winds would follow if left to 

 obey the forces of diurnal rotation alone, as they would do were 

 diurnal rotation the sole cause of their easting. As these winds 

 approach the equator, the effect of diurnal rotation becomes more 

 and more feeble. But the table shows no such diminution of ef- 

 fect. They have as much easting between 5° and 0° as they have 

 between 80° and 25°. Nay, the southeast trades between the 

 equator and 5° K. — where, by the Halleyan theory, they should 

 have icesting — have as much easting (§ 842) as they have between 

 80° and 25° S. We can not tell how much the air is checked in 

 its easterly tendency by resisting agents, by friction, etc., but we 

 know that tendency is ten times stronger between 80° and 25° 

 than it is between 5° and 0°, and yet actual observations show no 

 difference in their course. This table reminds us that diurnal ro- 

 tation should not, until more numerous and accurate observations 

 shall better satisfy the theory than those half a million and more 

 now do, be regarded as the sole cause of the easterly direction of 

 the trade-winds. It suggests either that other agents are concern- 



* "Average Force of the Trade-winds," p. 857, vol. ii., Maury's Sailing Direc- 

 tions, 1859. 



