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 

 entitled, " An Account of some Experiments on the Torpedo.'''' The 

 inference, drawn from these by the author, is, that the electricity of 

 this animal is, sui generis, and neither identical with common, or with 

 Galvanic, electricity. 



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. — 



On the dip of the Magnetic needle in London, in August, 1828. 



Experiments to determine the difference in the number of vibra- 

 tions, made by an Invariable Pendulum, in the Royal Observatory at 

 Greenwich, and in the house in London in ivhich Capt. Kater's ex- 

 periments tvere made. 



