WITH THE SALT WATER OP THE SEA. 513 



Even to navigators, an acquaintance with this subject may 

 sometimes be of use. Thus, for example, when entering a 

 creek in an unknown coast, they may easily ascertain whether 

 any streams of fresh water flow into it, by examining the com- 

 parative density of the water taken from the surface and from 

 below. 



These experiments appear to give countenance to the opi- 

 nion which supposes that the water at the surface of the sea 

 contains less salt than the water at the bottom. This may be 

 expected to take place in the neighbourhood of continents, at 

 least, whatever may be the case in the open ocean. During 

 winter, the difference is probably very considerable, as at that 

 season the rivers incessantly pour vast quantities of fresh wa- 

 ter into this great reservoir, while but a small portion is ab- 

 stracted by evaporation. In the Frith of Forth, the difference 

 between the dense water of summer and the diluted water of 

 the winter season, is as eighteen to sixteen, and that even as 

 far down as Prestonpans* 



Manse of Flisk, ) 

 llth March 1816. 1 



XXIV. 



