364 Philosophical Transactions of the 
through the straits of Gibraltar into the Mediterranean. This is in 
some measure counteracted by an under current, setting in an oppo- 
site direction, as has been inferred from wrecks that had sunk in the 
Mediterranean, having risen again in the Atlantic. But it also ap- 
pears to have been proved, that the evaporation from the Mediterra- 
nean exceeds the supply from rivers; and hence the under current 
must be less in quantity than the upper. Now, although this great 
evaporation would account for the loss of much of the water that 
runs Eastward through the straits, yet the salt which that water holds 
‘in solution, must remain in the basin of the Mediterranean, or es- 
cape by some hitherto unexplained means of exit. 
To settle this point, Dr. Marcet planned a set of experiments on the 
density of the water at different depths, and obtained the aid of Capt. 
W. H.' Smith, R. N. to carry them into effect. The experiments 
were made, but Dr. Marcet died, before the specimens collected at 
the'different depths had reached England. A part of them were un~ 
luckily given by Capt. Smith, to persons seeking them from no other 
motive than simple curiosity, but a few were left to fall into the hands 
of Dr. Wollaston, who completed, by their aid, the investigation com- 
menced by Dr. Marcet. The comparison of these specimens shews; 
that the water, at great depths, in the Mediterranean, contains four 
times as much salt as that in the main ocean; while that at the sur- 
face, and at depths not greater than four hundred and fifty fathoms, 
is identical in its composition with the water of the latter. Hence an 
under current, of a fourth part of the velocity and equal area, or of a 
fourth part of the area and equal velocity, would carry back to the 
ocean all the salt brought in by the upper current. 
- We find but one paper of Sir H. Davy in this half volume. It is 
ontitled, “An Account of some Experiments on the Torpedo.” ‘The 
inference, drawn from these by the author, is, that the electricity of 
this animal is, swi generis, and neither identical with common, or with 
Galvanic, electricity. eae aati ae 
~The remainder of the papers are by living men of science. Among 
these, Capt. Edward Sabine, of the British Royal Artillery, one of 
the present secretaries of the Royal Society, stands most conspicu- 
ous; his contributions are three in number, viz.— Lips peng 
‘On the dip of the Magnetic needle in London, tn August, 1828. 
Experiments to determine the difference in the number of vibra- 
ons, m de by an Fnvariable Pendulum, in the Royal Observatory at 
Greenwich; and in the house in London in which Capt. Karer’s ex- 
gir aass De 
