1870.] 



Deep-sea Researches. 



181 



being N.E. by E. \ E. This was a retardation of more than a mile per 

 hour, as compared with the former observation ; and that it was not attri- 

 butable to the mere surface- action of the easterly wind, was clear from the 

 result of the next observation, which showed that the retardation extended 

 to a depth far below the influence of surface-action. — The "current-drag" 

 having been lowered to 100 fathoms' depth, the drift of the boat was 

 reduced to 0*857 mile per hour, or less than half its surface-drift ; its 

 direction was nearly the same as that of the surface-current, viz. E. by 

 N. \ N. The " current-drag " was then lowered to a depth of 250 fathoms ; 

 and in a short time the boat was seen to be carried along by it in a direction 

 (W.N.W.) almost exactly opposite to that of the middle m-current of the 

 Strait. The rate of outward movement of the boat was 0*400 mile per 



Station 64. 



Rate (per hour) and Direction of Movement of Surface-float and of Current-drag at 

 different Depths ; with Force and Direction of Wind. 



hour ; but from the considerations formerly stated (§ 39), it is clear that 

 the actual rate of the undercurrent must have exceeded that of the boat 

 on the surface. — The "cur rent drag" was then lowered down to a depth of 

 400 fathoms ; and again the boat was carried along in nearly the same 

 direction as in the previous experiments, namely N.W. \ N. ; but more 

 slowly, its rate of movement being 0*300 mile per hour. 



63. Thus, then, our previous deductions were now justified by a con- 

 clusive proof that there was at this time a return-current in the mid- 

 channel of this narrowest part of the Strait, from the Mediterranean 

 towards the Atlantic, flowing beneath the constant surface-stream from 

 the Atlantic into the Mediterranean ; and it will be shown hereafter 

 (§ 115), by a comparison of all the results of our observations, that a 

 strong presumption may be fairly raised for the constant existence of such 

 a return-current, though its force and amount are liable to variation. 



64. As the determination of the boundaries of this return-current, and 

 of the amount and conditions of its variation, could only be effected by 

 multiplied simultaneous observations at different points, with ample license 

 as to time, neither of which fell within the scope of the present Expedi- 

 tion, we were obliged to content ourselves, as regards this locality, with 

 what we had found ourselves able to accomplish ; and at the conclusion of 

 this day's work we proceeded westwards under easy steam, so as to be able 



