Royal Society. . 379 



Care was taken that the specimens of wood which were the subjects 

 of experiment were sound and dry, and free from any large knots ; 

 and their correct dimensions were ascertained by an improved kind 

 of callipers. In every specimen two indexes were attached ; one a 

 few inches from the end fixed in the clamp, and the other at a small 

 distance from the attachment of the lever to which the straining 

 power was applied ; and the length of the bar subjected to torsion 

 was estimated by the distance of the points of attachment of the in- 

 dexes. A pivot was fixed at the supported end of the bar, in the line 

 of its axis. The author gives the following rule for finding the deflec- 

 tion of a prismatic shaft — namely, that it is equal to the product of 

 the straining power into the square of the radius by which it acts, and 

 into the length of the shaft divided by the modulus of torsion, into the 

 fourth power of the side of the square shaft. He then gives a table 

 of the modulus of torsion in different woods, which he finds to vary 

 from about nine to thirty thousand pounds, and to follow nearly the 

 order of the specific gravity. In the metals, the modulus of torsion 

 is one-sixteenth of the modulus of elasticity. 



"On the Water of the Mediterranean." By W. H. Wollaston, 

 M.D. V.P.R.S. 



The late Dr. Marcet, in his examination of sea-water, of which he 

 has given an account in the Philosophical Transactions for 1819, had 

 been unable, for want of a sufficient number of specimens of water 

 taken at various depths in the Mediterranean, to draw any certain 

 inference as to what becomes of the vast amount of salt brought into 

 that sea by the constant current which sets in from the Atlantic 

 through the Straits of Gibraltar, and which, on the evaporation of the 

 water, must either remain in the basin of the Mediterranean, or 

 escape by some hitherto unexplained means. In the hope of obtain- 

 ing further evidence on this question, he had requested Captain 

 Smyth, R.N. who was engaged in a survey of that sea, to procure 

 specimens of water from the greatest accessible depths. The speci- 

 ipens collected by Captain Smyth were, in consequence of Dr. Mar- 

 cct's death, given to other persons and applied to other objects. Dr. 

 WoUaston, however, fortunately obtained the three remaining bottles 

 of the collection. The contents of one of these, taken up at about 

 fifty miles within the Straits, and from a depth of 670 fathoms, was 

 found to have a density exceeding that of distilled water by more than 

 four times the usual excess; and accordingly it left upon evaporation 

 more than four times the usual quantity of saline residuum. The re- 

 sult of the examination of this specimen accords completely with the 

 anticipation that a counter-current of denser water might exist at 

 great dejiths in the neighbourhood of the Straits, capable of carrying 

 westward into the Atlantic as much salt as enters into the Mediter- 

 ranean with the eastern current near the surface. If the two currents 

 were of equal breadth and depth, the velocity of the lower current 

 need only be one-fourth of that of the upper current, in order to pre- 

 vent any increase of saltness in the Mediterranean. 



Feb. fith.— A pajjcr was read, intitled, " On the stability and ca- 

 pacity of recUngular flouting bodies," being a continuation of u former 



