Feb. 23, 1871] 
NATURE 
335 

of arotation, so as to carry on the tube into the dark cham- 
ber. A repetition of the making and unmaking of the 
magnet brings out the second tube, and shuts it up again; 
and another repetition does the like with the third tube. This 
apparatus, with a deep-sea lead attached to it, is suspended by 
an insulating cable that contains the wires whereby it is connected 
with the battery in the vessel. Keing lowered down to any desired 
depth, the circuit is completed, the magnet made, and one of 
the tubes exposed for as long a time as may be wished ; the cir- 
cuit is then broken, the magnet unmade, and the tube shut up 
again. The second tube may be exposed fora longer time in 
the same place, or the apparatus may be lowered to a greater 
depth, at which the experiment may be repeated’; and the third 
tube may then be dealt with in like manner.—The committee 
having been satisfied with the performance of Mr. Siemens’ 
apparatus, it had been arranged that trial should be 
made of it, and also of his Differential Thermometer, now 
provided with an improved Galvanometer; and he had 
undertaken to send out a qualified assistant to take charge of 
these instruments during the Mediterranean Cruise. The 
declaration of war between France and Germany, however, 
unfortunately interfered with this arrangement ; the assistant (a 
German) being recalled to his own country, and no other com- 
petent person being available on a short notice. Under these 
circumstances it was thought better that the Differential Ther- 
mometer should not be sent out ; but it was hoped that such a 
trial might be given to the Photometric Apparatus as should at 
any rate determine whether satisfactory results might be antici- 
pated from its use, or whether any modifications in its construc- 
tion might be needed. The apparatus was sent out to Gibraltar 
under charge of Dr. Carpenter, and was got into working order 
by his son and himself in Gibraltar Harbour. It proved, how- 
ever, that the action of sea-water on the bearings, —increased as 
this was by the galvanic current arising out of the contact of iron 
and brass in them,—so embarrassed its mechanical arrangements, 
that no fair trial could be made of its photometric efficiency. 
But the experiment served the important purpose of showing the 
weak points of the apparatus ; and neither Mr. Siemens nor Dr. 
Carpenter entertains any doubt that it may be so reconstructed 
as to answer the purpose for which it was devised. 
The work of this year’s Expedition was divided, according 
to the plan originally marked out, into two Cruises: the First to 
examine the Deep-sea bottom between Falmouth and Gibraltar ; 
the Second to make the like examination of the western basin of 
the Mediterranean between Gibraltar and Malta, and to determine 
its Physical and Biological relations to the Atlantic,—with 
special reference to the Gibraltar Current. The First Cruise was 
under the scientific direction of Mr. Gwyn Jeffreys, who was 
accompanied by a young Swedish naturalist, Mr. Josua Lindahl, 
of the University of Lund, as Zoological Assistant ; whilst Mr. 
W. L. Carpenter, as before, took charge of the Chemical 
department, —his special work, on this occasion, being the deter- 
mination, by volumetric analysis, of the proportion of chlorine 
in samples of Atlantic water taken from the surface, the bottom, 
and from intermediate depths, so as to serve as a basis of com- 
parison with similar determinations of Mediterranean water. In 
the Second Cruise it had been arranged that Dr. Carpenter and 
Prof. Wyville Thomson should co-operate as before ; but the 
latter being unfortunately prevented by serious illness from taking 
part init, the whole charge of this Cruise rested with Dr. Car- 
penter. He was fortunately able to retain the assistance of Mr. 
Lindahl ; and the chemical work was continued (as in the Third 
- Cruise last year) by Mr. P. H. Carpenter ; Mr. Laughrin through- 
out acted as dredger and sifter. 
[For the exceedingly interesting and valuable zoological details 
of the various dredging-hauls, we .must refer our readers to 
the report itself. ] 
Throughout the whole of this cruise the temperature of the 
' sea-bottom was taken by the protected Miller-Casella Ther- 
mometers in nearly every sounding. As, for the reason already 
mentioned, no extreme depths were sounded, and as the general 
rate of the diminution of temperature on the margin of the 
North-Atlantic basin seemed to have been established by the 
serial soundings taken in the expedition of the preceding year, 
it was not thought necessary to repeat these ; more especially as 
the variety of depths at which the Jéo/tom-temperature was 
ascertained gave adequate data for comparison with the results 
then correlated. It will be shown hereafter that this comparison 
leads to some very interesting conclusions, fully confirming the 
view advanced in the last report as to the slow northward moye- 


ment of an upper stratum of warm water 700 or Soo fathoms in 
depth, and of the southward movement of the whole deeper 
stratum, bringing water of an almost icy coldness from the 
Arctic basin into the temperate and even the intertropical zone. 
During the whole of this expedition the temperature of the 
surface of the sea was ascertained and recorded every two hours, 
both by day and by night ; as were also the readings of the Dry and 
Wet-bulb Thermometers, which were placed in a small penthouse 
on deck, in which they were freely exposed to the surrounding 
air, but secluded from direct or reflected solar heat. The tem- 
perature of the svrface-water, from the time of our leaving the 
British Channel in lat. 48° N. to our turning the corner of Cape 
St. Vincent in lat. 36° 50’ N., increased at a rate which bore a 
pretty regular proportion to the Southing. Thus, at the “chops 
of the Channel,” it averaged 62° for five days ; whilst, by the 
time we approached Cape St. Vincent, it had gradually risen to 
above 69°. After passing that point, however, we found both 
the suxface and the dottom-temperatures to present certain varia- 
tions, which, though not considerable in themselves, proved to be 
of great interest when taken in connection with the peculiar con- 
dition of the edouchure of the Strait of Gibraltar. These points, 
however, will be more fitly discussed hereafter; and we shall 
now only notice a sudden 77se in surface-temperature of about 3° 
which showed itself as we turned the corner of Cape St. Vincent 
and entered the zorth side of the embouchure ; and a sudden /a// 
of nearly 6° (to 66°°4) which was encountered when we entered 
the mid-stream of the narrower part of the Strait as we proceeded 
towards Gibraltar. 
In the course of the first portion of the cruise between Fal- 
mouth and Lisbon (beyond which point Mr, W. L. Carpenter 
was unable to proceed), thirty-six quantitative determinations 
were made by volumetric analysis, of the amount of chlorine in 
as many samples of Atlantic water, taken (1) from the surface, 
(2) from the bottom at various depths, and (3) from various 
intermediate depths. The greater part of these, as will be 
shown hereafter, indicated a very close conformity to a 
uniform standard of density, as indicated by a specific gravity of 
1'0268, and a Chlorine proportion of 11°84 per 1000 ;* the chief 
departures being observable in the /ower density of the deepest 
waters, and in the occasional excess of density in the surface- 
waters. The former is doubtless attributable to the fact that the 
deepest water is essentially Polar, and therefore derives its more 
dilute character from that source. The latter we are inclined to 
attribute to the influence of slight concentration by evaporation. 
Second Cruise.—Leaving Gibraltar early in the morning of 
Monday, Aug. 15, we steamed out into the middle of the Strait, 
for the purpose of commencing our experiments on the Gibraltar 
current. The point selected by Capt. Calver (Chart of Strait 
of Gibraltar, Station 39) lay midway between Point Camero, 
which forms the south-eastern boundary of Gibraltar Bay, and 
Jebel Musa or Apes Hill, which lies opposite to it, at a distance 
of only 8 geographical (9} statute) miles, on the African coast, 
the Strait being here nearly at its narrowest ; and it was also 
that at which the greatest depth (510 fathoms) was indicated by 
the soundings marked on the Chart. With this depth our own 
sounding, which gave a bottom at 517 fathoms, agreed very 
closely ; and having thus at once found the position most advan- 
tageous for our work, that position was precisely determined by 
angles taken by sextant from the ship between conspicuous 
objects on the shore. The do/tom-temperature obtained in the 
first sounding was between 5° and 6° Azgher than that which had 
been met with at corresponding depths on the bed of the Atlantic 
about 100 miles to the westward ; whilst the szface-temperature 
was lower by from 1°*3 to 2°, as will be seen by the following 
comparative statement :— 
Surface Bottom 
Station, Depth, temperature, temperature. 
° ° 
Strait of Gibraltar 39 517 70" 55'5 
Atlantic... on 31 477 13 50°5 
Atlantic .. ace 32 651 70'5 50°0 
Atlantic ... ane 33 554 720 497 
Atlantic... ase 34 414 717 500 
This striking difference led us to take a set of seta/ soundings 
at intervals of 50 fathoms, and these gave a result, which, though 
it appeared anomalous at the time, was afterwards fully ex- 
plained, and proved to be of unexpected import. The tem- 
perature fell, at 50 fathoms from the surface, to 56°; at 100 
* The proportion here adopted,—the number of Grammes of Chlorine to 
1000 Cubic Centimetres of water, is that employed by Prof. Forchhammer 
in his elaborate Memoir on the Composition of Sea Water (Phil. Trans. 1865), 
