March 23, 1871] 
NATURE 
417 
——$—$<<___ 


a depth of 250 fathoms; and ina short time the boat was seen 
to be carried along by it in a direction (W.N.W.) admost exactly 
opposite to that of the middle ¢-current of the Strait. The rate 
of outward movement of the boat was 0-400 mile per hour ; 
but from the considerations formerly stated, it is clear that the 
actual rate of the under-current must have exceeded that of the 
boat on the surface. The ‘‘current-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. 3 N.; but more slowly, its rate of movement 
being 0°300 mile per hour. 
ee ae 
200 Fath. 
a) 
South 
Thus, then, our previous deductions were now justified by 
a conclusive proof that there was at this time a return-current in 
the mid-channel of this xarrowest 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, 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. 

As the determination of the boundaries of this return- 
| current, and of the amount and conditions of its variation, could 
| 
Wind * 
—--—--- t 
‘Force Bios 
| 
z] 



Wind 
Sve 3: 
force 5 
Fic. 2—Rate (per hour) and Direction of Movement of Surface-Float, and of Current-Drag at different Depths ; with Force and Direction of Wind 
in No. 3. 
only be effected by multiplied simultaneous observations a | 
different points, with ample license as to time, neither of whicht 
fell within the scope of the present expedition, 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 to resume our experiments the next morning in the s/a//owest 
part of the Strait. 
The average surface-temperature of the mid-stream during 
Our outward passage through the Strait proved to be 66°; thus 
corresponding exactly with what we had found it to be on our | 
inward passage seven weeks previously. This depression, as 
compared with the surface-temperature of the Strait itself nearer 
the shore, both north and south, and with the temperature of 
the Mediterranean to the eastward and that of the Atlantic to 
the westward, is extremely remarkable. We shall hereafter 
inquire how it is to be explained. 
The breadth of the Channel between Capes 
and Trafalgar is about twenty-three nautical or twenty-six 
and a half statute miles. Its northern half is much shallower 
than the southern, the 100-fathom line off the Spanish coast 
running at about twelve miles’ distance from Cape Trafalgar ; 
whilst along the African coast it keeps much nearer the 
hore, being at only two miles’ distance from Cape Spartel. 
Between these two lines, the greatest depth marked in the 
chart is 194 fathoms; and this occurs off Cape Spartel, at 
less thana mile from the 100-fathom line, Between this and 
the opposite border of the deeper channel, the depths vary 
from 130 to 180 fathoms; the abruptness of the differences at 
neighbouring points indicating a rocky bottom, of which we 
soon had unpleasant experience, 
Spartel | 
(No Wind in Nos 1, 2.) 
SCIENTIFIC SERIALS 
In the Yournal of Botany for March we find a continuation 
of the useful catalogue of new species of Phanerogamous plants 
published in Great Britain during the year 1870, and of Mr. 
Hiern’s paper on the forms and distribution over the world of 
the Batrachian section of Ranunculus. Dr. Dickie contributes 
| a paper on the distribution of Algze, and Mr. A. G. More the 
commencement of a Supplement to Bromfield’s ‘‘ Flora Vec- 
tensis.” Short notes, reviews, and reports of Societies fill up 
the number, 
THE American Naturalist for February contains several inte- 
resting papers. Among them is one on the ant-lion (AZyrmeleo 
immaculatus), a Neuropterous insect, by Mr. J. H. Emerton, 
with drawings of its matamorphoses ; one on the resources and 
climate of California, by Rev. A. P. Peabody; notes on some 
birds in the Museum of Vassar College, by Prof. Jas. Orton; a 
short account of the spores of Lichens, by Mr. H. Willey ; the 
Sperm Whales, giant and pigmy, by Dr. Theodore Gill, illus- 
trated with numerous drawings, including the skull of Cal/ienathus 
simus and Physetir macrocephalus. The Natural History Mis- 
cellany comprises also several shorter papers of much interest, 
including one on the morphology and ancestry of the King 
Crab, by the editor, Dr. A. S. Packard, jun. 
THe March number of the Geological Magazine (No. 81) 
commences with a long article by Mr. James Croll ‘‘On the 
Determination of the Mean Thickness of the Sedimentary 
Rocks of the Globe.” The author <lisusses the different methods 
which have been adopted in order to obtain an approximate esti- 
mate of the time occupied in the fo oation of the sedimentary 
| rocks, and remarks that in all these researches it must be borne 
