356 THE PHYSICAL GEOGKAPHY OF THE SEA. 



should reduce tlie average knots per hour to the average sjDeed of 

 a mean ship sailing through average "trades" in each ocean, with 

 the wind impinging upon her sails at the same angle for all three, 

 as, for example, just abaft the beam, as in the Korth Atlantic. 



1007. Let us apply to the average speed through the South 

 Atlantic and Indian Ocean such a correction. Through the for- 

 mer, the wind is aft ; through the latter, quartering. If we allow 

 two knots for the one, and one for the other, we shall not be 

 greatly out. Applying this correction, we may state the speed 

 of a mean ship sailing with average trades just abaft the beam to 

 be as follows : 



Through the N.E. of the Atlantic . . 6^ knots per hour. 

 " " S.E. " " 8 " " " 



" "S.E. " Indian Ocean, 8 " " " 



I do not take into this comparison the force of the [N'.E. trades 

 on a S.S.E. course (p. 355), because the winds along this route are 

 known not to be as steady as they are farther away from the Af- 

 rican coast. Thus it is clearly established that the S.E. trades are 

 stronger than the N.E., and so tliey should he, if there he a crossing 

 of winds in the calm belt of Capricorn. 



The counter-trades of the southern hemisphere move, as before 

 stated, toward their pole more steadily and briskly than do the 

 counter-trades of the northern hemisphere. To give an idea of 

 the difference of the strength of these two winds, I cite the fact 

 that vessels sailing through the latter, as from New York to En- 

 gland, average 150 miles a day. Along the corresponding lati- 

 tudes through the former, as on a voyage to Australia, the average 

 speed is upward of 200 miles a day. Consequently, the counter- 

 trades of the southern hemisphere transport in given times larger 

 volumes of air toward the south than our counter-trades do to- 

 ward the north. This air returns to the tropical calm belts as an 

 upper current. If, descending there, it feeds the trade-winds, tlien, 

 the supply being more abundant for the S.E. trades than for the 

 N.E., the S.E. trades must be the stronger; and so they are ; ob- 

 servations prove them so to be. 



Thus, the crossing of the air at the calm belts, though it may 

 not be proved, yet it is shown to be so very probable that the onus 

 of proof is shifted. It now rests with those who dispute the cross- 

 ing to prove their theory the true one. 



