Feb, 23, 1871 | 

rate of the stratum in which the drag hangs to a degree exceeding 
the retardation of the movement of the boat, may be safely pre- 
dicated ; (3) that when this retardation is so considerable that the 
boat moves very s/ow/y in the direction of the surface-current, it 
may be inferred that the stratum in which the drag is suspended 
is either stationary, or has a slow movement in the opposite 
direction ; (4) that if the boat should remain s¢etonary, a force 
must be acting on the ‘‘ drag” which is equal, and in the con- 
trary direction, to that of the upper current upon the boat and 
suspending line ; so that the existence of a counter-current is 
indicated, having a rate as much /ess than that of the surface- 
current as the resisting surface presented by the ‘‘drag”’ is 
greater than that offered by the boat and upper part of the sus- 
pending line ; (§) that if the boat should move in a direction 
opposed to that of the surface-current, a motion is indicated in 
the stratum in which the ‘‘ drag” hangs, which will correspond 
in direction with that of the boat, and which will exceed it in 
vate, the effect of the ‘‘ drag” upon the boat being partly neutra- 
lised by the antagonistic drift of the surface-current. 
Now our first set of experiments with the ‘‘current-drag” 
gave the following results :— 
(1.) The surface-movement being first tested in the manner 
already described, its rate was found to be 2°88 nautical miles 
per hour, and its direction E. by S. }S. The wind was W. by 
N., with a force of 4. 
(2.) The ‘‘ drag” having been lowered down to a depth of 100 
fathoms, the rate of movement of the boat from which it was 
suspended was reduced to 1°550 mile per hour, or rather more 
than half the surface-movement. Its direction was E. 4 S. 
Taking into account the action of the wind and surface-current 
on the boat, it may be safely affirmed that at 100 fathoms the 
rate of the current was reduced to /ess than one half. 
(3-) The drag having been lowered down to a depth of 250 


NATURE 337 
o 

fathoms, the boat remained nearly stationary, its vate of move- 
ment being reduced to 0°175 mile per hour, while its direction 
(S.E. 4 E.) was slightly altered to the southward, though still 
easterly. From this we felt ourselves justified in inferring that 
the 250-fathoms’ stratum had a movement in the reverse direction 
acting on the current-drag with a force almost sufficient to neu- 
tralise the action of the upper stratum on the boat and suspending 
line. And this inference ‘s strengthened by the extraordinary 
density of the water of this stratum, and is fully justified by the 
results of the experiments which we made on our return-voyage, 
While these experiments were in progress, we had the 
pleasure of seeing the Channel Fleet, which was expected to meet 
the Mediterranean Fleet at Gibraltar, come in sight beyond Cape 
Tarifa ; its approach having been indicated, long before even the 
tops of the masts of the vessels composing it showed themselves 
above the horizon, by the number of separate puffs of smoke 
which the experienced eye of our Captain enabled him to dis- 
tinguish. As soon as all possibility of doubt was removed b 
the appearance of the masts, Capt. Calver communicated ‘Fleet 
in sight” by signals to the Admiral in Gibraltar Harbour ; our 
position being such that we could be seen by him, though the 
Fleet could not. In due time, the massive hulls of the ironclads 
rose above the horizon, and whilst we continued at our work 
all passed us in sailing order, at a distance of not more than a 
couple of miles, the ill-fated Caftain being the chief object of 
interest. A few hours later, the A/onarch, which had been de- 
tained for repair, but whose passage had been made in a shorter 
time by the free use of her steam-power, came in sight, and 
passed on in solitary grandeur to join the fleet, now united in 
Gibraltar Bay. 
The whole of our first day having been consumed without 
our being able to work the ‘‘ current-drag” in the deepest stra- 
tum, we anchored for the night near Point Carnero, with a view 

West == — — 
=A Force 3. 


Fic. 2-Rate(per hour) and Direction of Movement of Surface-Float, and of Current-Drag at different Depths ; with F. rce and D'rection of Wind 
to resuming our experiments on the following morning. We then 
ran out to a spot almost precisely identical with that which had 
been our starting-point on the previous day ; and commenced as 
before, by testing the rate and direction of the surface-movement. 
Its rate proved rather slower, being 2°40 miles per hour, instead 
of 2°88 ; and its direction was E. by N., instead of E. by S. 3S. 
Both differences seemed to be accounted for by the difference in 
the force and direction of the wind ; which, having been W. by 
N. with a force of 4 on the previous day, was now W. 45S. with 
a force of only 2. The “drag” was then lowered to a depth of 
400 fathoms ; but our expectation that it would there encounter 
a westerly (or outward) current sufficiently strong to carry the 
boat in that direction in spite of the antagonistic movement of 
the easterly (or inward) surface-current, was not verified on this 
occasion ; for the boat slowly drifted in an E. } N. direction, its 
rate being 0°650 mile per hour. Whether this result should be 
taken to indicate a stationary condition of the deep stratum, or a 
slight movement in either direction, can scarcely be affirmed with 
positiveness ; but from the indication afforded by the specific 
gravity of the water taken up from this depth, it would seem 
probable that the general movement of this stratum was at this 
time rather westerly, or in conformity with that which we attri- 
buted to the intermediate stratum, though at a slower rate. It 
will be shown hereafter that a decisive proof of such a move- 
ment was obtained on a subsequent occasion. 
Thinking it expedient to postpone the further prosecution of 
this inquiry until our return-voyage,—when we should be able to 
repeat our experiments, not only at this narrow end of the 
Strait where it enters the Mediterranean Basin, but also at that 
shallowest portion to the westward, where the Strait opens out 
into the Atlantic, —we put steam on before mid-day, and entered 

the basin of the Medite:ranean, directing our course in the first 
instance to the spot (lat. 36° o’ N., long. 4° 40’ W.) at which the 
sample of bottom-water had been obtained by Admiral Smyth, 
which, when analysed by Dr. Wollaston, was found to possess 
the extraordinary specific gravity of 11°288, and to yield a per- 
centage of 17°3 of salt.* As we were within sight of both 
shores, and could distinguish several remarkable mountain- 
summits which were accurately laid down on our charts, 
the bearings of these enabled the situation of the ship to be 
determined with great precision ; and Captain Calver undertook 
to place her within a mile of the point at which Admiral 
Smyth’s observation had been taken. Having reached this, 
we took our first sounding in the Mediterranean, and awaited 
the result with no little interest. The depth proved to be 586 
fathoms, or 84 fathoms less than that given by Admiral Smyth’s 
sounding; but as the latter was not taken on the improved 
method now adopted, and as its correctness may have not im- 
probably been affected by the strength of the easterly current 
which is here very perceptible, the discrepancy can scarcely 
be considered as of any real account as showing that 
the two points were otherwise than nearly coincidentt The 
* Phil. Trans. for 1829, p. 29 ; and Admiral Smyth's ‘* Mediterranean,” 
pp. 128—130. Pek 
+ Thus Admiral Smyth states (‘‘ Mediterranean,” p. 159) the depth in mid- 
channel between Gibraltar and Ceuta to be gso fathoms; whereas it is now 
known to be but little more than 500 fathoms. “‘ A little farther to the east- 
ward,” he says, “‘there is no bottom with 1,000 fathoms of line up-and-down 
upwards of 1,300 payed out) ;” whereas the greatest depth as far east as 
alaga Bay is now known not to exceed 750 fathoms. These errors are 
noticed in no invidious spirit, but merely to prevent their perpetuation, 
Admiral Smyth doubtless made the very best use of the means at his dis- 
posal ; but a far more satisfactory method has now entirely superseded that 
formerly adopted. 
