416 
NATURE 
[March 23, 1871 

dispersed as we approached it, so that we could distinctly trace 
the outline of its cone, save where this was obscured by a con- 
stantly shifting semi-transparent cloud. Whether this was a light 
smoke given off from the cone, or a film of vapour condensed by 
the contact of a current of warm moist air with the colder surface 
of the mountain-summit, We were unable to distinguish, though 
we watched it with great interest during the whole afternoon. 
We steamed quietly along the Sicilian coast during the night, so 
that sunrise the next morning found us in the narrowest part of 
the Strait of Messina, between Messina and Reggio; and we 
shall not easily forget the beauty of the spectacle we then beheld 
on either shore. Passing through the once-dreaded Charyhdis, 
the dangers of which are rather poetical than real, and leaving on 
our right the picturesque castle-crowned rock of Scylla, we passed 
out of the ‘‘ Faro,” which narrows at its northernmost extremity 
to about three and half miles, into the open sea to the north of 
Sicily, studded by the Lipari Isles ; and steered direct for Strom- 
boli, stopping at 10 A.M. to take a sounding (station 61). This 
gave us a depth of 392 fathoms, and a bottom temperature of 
55°'7, which afforded no indication of unusual elevation. Here 
again we found the density of the bottom-water scarcely in excess 
of that of the surface-water ; and it was even lower than the 
surface-water in another sounding taken somewhat further on, 
(station 62), and at a depth of 730 fathoms, which gave a bottom 
temperature of 55°°3. 
Sp. Gr. Chlorine. 
Surfaces. esha se . 10281 21°32 
Bottom, 392 fathoms. . . 1°0282 21.36 
Bottom, 730 fathoms. . . 1°0280 21°22 
This result, again, surprised us much at the time ; but we are 
now inclined to attribute it to the decrease of surface-evaporation, 
consequent upon the marked decrease in the heating-power of 
the sun, which showed itself in the change of the relative tempera- 
tures of the sea and air. For whilst for some days before we 
put into Malta, the surface-temperature of the sea had ranged 
between 76° and 78°, and the temperature of the air had been 
usually about 1° Azgher, we now found that while the surface- 
temperature of the sea ranged between 73°°6 and 76°°6, the tem- 
perature of the air was between 2° and 4° /ower. This difference 
continued to show itself nearly all the way to Gibraltar ; the daily 
averages of the surface-temperature of the sea ranging between 
73°71 and 75°°6, whilst those of the temperature of the air ranged 
between 68°°5 and 72°°0. We now approached the rugged 
cone of Stromboli, from the summit of which there was 
constantly issuing—as has been the case since the time 
when the neighbouring island of Hiera was fabled to be 
the workshop of Vulcan—a cloud of smoke, indicative of 
active changes in the molten depths beneath. Of this 
activity, however, we had found no special indication in the 
temperature-soundings taken nearest to the island. Whether the 
general prevalence in the neighbourhood of Sicily of a bottom- 
temperature averaging about a degree above that of the western 
part of the Mediterranean, is due to subterranean heat, is a 
question which can only be determined by a larger number of 
observations than we had the opportunity of making. As we 
neared Stromboli, we were much struck with the height to which 
the energetic industry of its inhabitants had carried the vine- 
cultivation all round the cone, save on two slopes looking N. W. 
and S.E., over one or other of which there is a continual dis- 
charge of volcanic dust and ashes. Although no flames were 
visible during daylight, we could distinctly perceive occasional 
flashes as night cameon, Our course was now laid straight for 
Cape de Gat, which we passed on the 27th of September, 
arriving at Gibraltar on the evening of the 28th. The only 
scientific observations which we had the opportunity of making 
during this part of our voyage were confirmatory of those which 
we had made at the commencement of our Mediterranean cruise 
as to the lower temperature and inferior density of the surface- 
water, both which we attribute to the inflow from the Atlantic. 
Having taken in at Gibraltar as much coal as we could carry, 
we left the harbour at 9 A.M. on the 30th September, and pro- 
ceeded at once towards the scene of our previous observations. 
Wethought it worth while, however, to take a sounding in our 
way towards this, near the roo-fathom line (station 63), for the 
sake of ascertaining the temperature and specific gravity of the 
bottom-water, The depth was found to be 181 fathoms, showing 
that the slope from the shallow to the deep portion of the 
channel is here very rapid. The bottom-temperature was 54°°7, 
that of the surface being 68°; and the specific gravity of the 

bottom-water was 1'0280, that of the surface being 1'0271. 
This bottom-water thus agreed closely in both particulars with 
that of the deep mid-channel, as ascertained in our first set of 
observations, and confirmed by our second. 
We then steamed out to a point (station 64) nearly identical 
with that from which our previous investigations had been carried 
on; and commenced our work with a temperature-sounding. 
The surface-temperature (65°°6) proved to be here /ess by 2°"4 
than it had been found to be at station 63; and this although it 
was taken an hour later in the forenoon, when an increase might 
have been expected. It thus corresponded closely with what had 
been previously found to be the average temperature of the Strait 
iu mid-channel, both during the first approach at Gibraltar from 
westwards, and during our own experiments at the commence- 
ment of the Mediterranean Cruise; and the continuation of the 
like observations during the remainder of the day and ensuing night 
gave thesame remarkable result, the rationale of which will be 
considered hereafter. ‘The depth was somewhat less than at the 
neighbouring station 39, being 460 fathoms instead of 517 ; but 
the bottom temperature was a little lower, being 54°°7 instead of 
55°°5. The respective specific gravities of the surface and 
bottom waters, and of that of the intermediate stratum of 250 
fathoms, were found to coincide almost exactly with those pre- 
viously determined, as the following comparative statement 
shows :— 
Sp. Gr. Sp. Gr. 
Station 39 Station 64 
Surface %% 2 + Sy = "o27er 1027.1 
250 fathoms . . . . 1029°3 1029'2 
ottoman) 505) vs) is ee OZ Sm 1028°3 
Now the density of the Jdo/tom-water here corresponds so 
exactly with that which prevails over the defer bottom of the 
western basin of the Mediterranean, whilst it so considerably 
exceeds that of the doffom as well as of the surface water of the 
Atlantic, that we cannot fail to recognise it as belonging to the 
Mediterranean basin; so that, if it has any motion at all, we 
should expect that motion to be from east to west. Still more 
certainly may this be affirmed of the zzéermediafe stratum, the 
density of which corresponds with that of the bottom waters 
of the sha/lower part of the Mediterranean basin ; the greatest 
depth (586 fathoms) at which such water was obtained, being at 
station 40, the nearest point to the Strait from which a specimen 
of bottom water was obtained. And it may be further predi- 
cated that a stratum of water of a density of 1029°3 could not 
overlie water of the density of 10281, unless it moved over 
the stratum below, that is, unless (1) the two strata were moving 
in, opposite directions, or (2) were moving at different rates in 
the same direction, or (3) the upper stratum were in motion in 
either direction, and the lower stratum were stationary. It will 
presently appear that the second of these conditions is the one 
which obtains in the present case. 
We now proceeded to repeat our experiments with the ‘* cur- 
rent-drag,” with the view of obtaining, if possible, unequivocal 
evidence of the existence of that westerly under-current, which 
so many considerations combined to render probable. The di- 
rection of the wind during this set of experiments was from the 
east, or opposite to that of the surface-current ; and its force (3 
to 4) was sufficient, by its meeting the current, to produce a con- 
siderable swell, which necessitated the employment of a larger 
boat, and rendered it unsafe to allow her to drift without men. 
The sectional area of the boat was therefore greater than 
on the former occasion, giving the in-current a stronger hold 
upon her ; but, on the other hand, the surface she presented 
to the wind was also greater ; and as this acted in the opposite 
direction, the latter increase might be considered to neutralise 
the former, or even rather to exceed it, so as to render the 
boat more capable of being carried westwards by the ‘‘ current 
drag,” if this should be acted on by an outward under- 
current. The rate of surface-current was tested as before, 
and proved to be 1°823 mile per hour, its direction 
being N.E. by E. 4 E. This was a retardation of more than a 
mile per hour as compared with the former observation ; and 
that it was not attributable 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 /ess than half its surface-drift ; 
its direction was nearly the same as that of the surface-current, 
viz., E. by N. 4. N. The ‘‘ current-drag” was then lowered to 
