346 Dr George Buist on the 



withdrawn and stored away at the time it might have proved 

 superfluous or inconvenient, is reserved, and rendered back 

 so soon as it is required ; and the cold of night, and rigor of 

 winter, are modified by the heat given out at the point of 

 condensation, 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 

 great object of the Creator apparently for an indefinite time 

 to maintain, and the arrangements for equalizing tempe- 

 rature, the equilibrium of saltness, be disturbed in certain 

 portions of the sea, and that of moisture underground in the 

 warmer regions of the earth. To prevent this, checks and 

 counterpoises interpose just as their services come to be re- 

 quired. It could scarcely be imagined that in such of our 

 inland seas as were connected by a narrow strait with the 

 ocean, and were thus cut off from free access to its waters, the 

 supply of fresh water which pours into them from the rivers 

 around, would exactly compensate the amount carried away 

 by evaporation ; salt never rises in steam, and it is the pure 

 element alone that it is drawn off. We have in such cases 

 as the Black and Baltic seas an excess of supply over what is 

 required, the surplus in the latter case flowing off through the 

 Dardanelles, in the former through the Great and Little Belts. 

 The vapour withdrawn from the Mediterranean exceeds by 

 about a third the whole amount of fresh water poured into it ; 

 the difference is made up by a current through the Straits of 

 Gibraltar in the latter ;* and a similar arrangement, modified 

 by circumstances, must exist in all cases where conditions 

 of things are similar, — the supply of water rushing through 

 the strait from the open ocean being in exact proportion to 

 the difference betwixt that provided from rain or by rivers, 

 and that required by the drain of vapour. Seas wholly iso- 

 lated, such as the Caspian and the Dead Sea, attain in course 

 of time a state of perfect equilibrium — their surface becoming 

 lowered in level and diminished in area, till it comes to be ex- 

 actly of the proper size to yield in vapour the whole waters 



* Captain Smith's excellent work on the Mediterranean, published since the 

 above wa9 written, throws much valuable light on all these subjects. 



