TRANSACTIONS OP THE SECTIONS. 13 



the tepid waters of the tropical seas. With the first of these, which has been so 

 fully treated of in the Geological Section, we at present have no concern ; and it is 

 to the second that attention is proposed to be directed. One cubic inch of water, 

 when invested with a sufficiency of heat, will form one cubic foot of steam — the 

 water before its evaporation, and the vapour which it forms, being exactly of the 

 same temperature, though in reality, in the process of conversion, 1700 degrees of 

 heat have been absorbed or carried away from the vicinage, and rendered latent or 

 imperceptible ; this heat is returned in a sensible and perceptible form the moment 

 the vapour is converted once more into water. The general fact is the same in the 

 case of vapour carried off by dry air at any temperature that may be imagined, for 

 down far below the freezing-point evaporation proceeds uninterruptedly, or is raised 

 into steam by artificial means. The air, heated and dried as it sweeps over the 

 arid surface of the soil, drinks up by day myriads of tons of moisture from the sea, 

 as much indeed as would, were no moisture restored to it, depress its whole surface 

 at the rate of 4 feet annually over the surface of the globe. The quantity of heat 

 thus converted from a sensible or perceptible to an insensible or latent state is 

 almost incredible. The action equally goes on, and with the like results, over the 

 surface of the earth as over that of the sea, where there is moisture to be withdrawn. 

 But night and the seasons of the year come round and the surplus temperature thus 

 withdrawn and stored away at the time it might have proved superfluous or in- 

 convenient, is reserved, and rendered back as soon as it is required ; and the cold of 

 night and rigour of winter are modified by the heat given out at the point of con- 

 densation, by dew, rain, hail, and snow. There are, however, cases in which, were 

 the process of evaporation to go on without interruption and without limit, that 

 order and regularity might be disturbed, which it is the intention of the Creator, 

 apparently for an indefinite time, to maintain, and in the arrangements for equalizing 

 temperature the equilibrium of saltness be disturbed in certain portions of the sea, 

 and that of moisture underground in the warmer regions of the earth. 



Thirty-six years ago Sir John Leslie pointed out that the waters discharged by 

 the rivers of southern Europe were not sufficient to supply the Mediterranean with 

 store enough for vapour for the countries on its shores, and that the immense 

 amount drawn off by the arid borders of Northern Africa, which from Alexandria 

 westward suppHed nota single rivulet, required to be provided forby an inward current 

 from the outer ocean through the Straits of Gibraltar. Founding apparently on 

 this. Sir Charles Lyell, in his geological work published in 1832, assumed the filling 

 up of the Mediterranean with salt ; and a doctrine about to be shown in conflict 

 with a first law of hydrostatics which nothing can upset, is still retained amongst 

 the dogmata of orthodox geology without anything whatever to support it. The 

 error seems to have been fallen into from the assumption that the water at the 

 surface of the sea would remain in its place exposed to the action of the sun until 

 evaporated up to the point of saturation, and only begin to descend on being 

 transformed into solid salt, in which condition it would remain of course accu- 

 mulating in the recesses of the sea. In point of fact, however, the instant the upper 

 stratum of a fluid becomes one atom lighter than that beneath, it inevitably begins 

 to descend, all other portions following it according as additional gravity is acquired 

 by them. So soon as this mass of brine grows high enough to run over the barrier 

 of the inland sea, it must, as a matter of necessitj% flow outwards to the external 

 ocean, where no such brine existed, and mingled with the average of the sea. It is 

 matter of easy demonstration, that without some such arrangement as this, the Red 

 Sea must long ere now have been converted into one mass of salt ; and its upper waters 

 at all events, being, on the other hand, known in realitj' to differ at present but little 

 in saltness from those of the southern ocean. Here we have salt water flowing 

 in perpetually through the Straits of Babelmandeb to furnish supplies for a mass of 

 vapour calculated, were the strait shut up, to lower the whole surface of the sea 

 8 feet annually, and even with the open strait, to add to its contents a propor- 

 tionate quantity of salt. But an under-current of brine, which, from its gravity, 

 seeks the bottom, flows out again to mingle with the waters of the great Arabian Sea, 

 where, swept along by currents, and raised to the surface by tides and shoals, it 

 is mingled by the waves through the other waters which yearly receive the enormous 

 monsoon torrents the Concan and the Ghauts supply, becomes diluted to the proper 



