Green-Mountain freeman. [volume] (Montpelier, Vt.) 1844-1884, 1871-07-26
carpenter on Mediterranean Currents

IN interesting communication In regard
10 the curronte .f tho N~-l..--.----------. s.-.-
lately been made IN various journals, by
DR.. William b. Carpenter, based upon the
result of his experiments made on board
the Porcupine during the deep-sea sound
ing surveys in the Mediterranean in the
past year. We have already given our
readers a synopsis Of the results obtained
in the summer OF 500 on board the Por-
cuplne, during the expeditions of which
Dr. Carpenter was also 4 member; and
although the work OF 1870 does not IN
clude drcdgings at such enormous depths
as three miles, 1t Is scarcely inferior IN
value One of the most important points
reached was the determination Of a deep
sea current in the Mediterranean running
TO the westward, as the counterpart of the
surface current from the eastward through
the straits. This had been suspected for a
long time, in view of the fact that cur
rent was continually entering the straits
from the Atlantic it being, of course,
readily inferred that this surface current
was to restore the level of the Mcditcrra-
mean, lowered by the immense amount of
evaporation. In the opinion of some the
CLCtl WIS HllLDi1 ~ NOltGulI1Lt liiE SIAL Vi
this inland sea and cause it to saturate the
lower strata, and perhaps even to form
sohd beds Of salt at the bottom. This
supposition, however, can easily be proved
to be untenabIe The method adopted by
the Porcupine party TO show the existence
of an outward under current consisted in
the use Of what was called the current
drag, an apparatus so constituted as to
present resisting surface so much larger
than that of the boat from which it was
suspended that although the latter might
tend to shove in the direction of the sur
face current, this could be counteracted by
the action Of the under-current upon the
drag. In some instances the effect was
simply to retard the velocity of the surface
current by that of a lower depth.
\ chemical examination of the water
brought up from great depths in the Med
iterranean proved, as suspected, that the
deep-sea water was more salt than that at
the surface, and that, consequently, the
tendency to saturation existed, but nothing
could be found to show the existence of
bed of salt at the bottom and strata Of
water Of less density were met with below
those of greater density. 1t Will, there
fore, be readily understood that the out
ward current in large part carries with it
the excess of salt produced by the surface
evaporation referred to. The cause of the
circulation itself is due, according to DIR.
Carpenter, to purely hydrostatie action.
which he explains as follows The water
of the Mediterranean is continually losing
by evaporation a larger amount than is
returned to it by rain or rivers, and con-
sequently the inflow from the Atlantic
must take place to keep up this level If
this inflow consisted of fresh-water the
total quantity of salt in the Mediterranean
would remain the same, and the density
would therefore undergo no increase. But
as the upper current of salt water brings
in certain quantity of salt, in addition
to that which the Mediterranean basin
previously contained, the density of this
water is increased, and 4 column Of it
reaching to any given depth becomes heay-
ier than corresponding column Of Attain
tic water. Consequently the excess of
downward pressure will displaee the lower
portion of the column of water, which will
flow outward as an under-current. The
withdrawal of portion Of the lower stra-
tum will produce a renewed reduction of
the surface level, taken In connection with
continued evaporation, and this will occa-