188 



the sky on the clouds. It is said, a great natu- 

 ralist, Sir Humphry Davy, thinks, that the tints 

 of different seas may very likely be owing to 

 different proportions of iodin. 



On consulting the geographers of antiquity 

 we find, that the Greeks were struck by the 

 blue waters of Thermopylae, the red waters of 

 Joppa, and the black waters of the hot-baths 

 of Astyra, opposite Lesbos*. Some rivers, the 

 Rhone for instance, near Geneva, have a decidedly 

 blue colour. It is said, that the snow waters, in 

 the Alps of Switzerland, are sometimes of an eme- 

 rald green approaching to grass green. Several 

 lakes of Savoy and of Peru have a brown colour 

 approaching black. Most of these phenomena of 

 coloration are observed in waters that are be- 

 lieved to be the purest, and it is rather from 

 reasonings founded on analogy, than from any 

 direct analysis, that we may throw some light 

 on so uncertain a matter. In the vast system 

 of rivers which we have traversed (and this fact 

 appears to me striking) the black waters are 

 principally restricted to the equatorial band. 

 They begin to be found about five degrees of 

 north latitude ; and abound thence to beyond 

 the equator as far as about two degrees of south 



* Pausanias, vol. 2, Messen., cap. 35 (Clavier's edit., p. 

 488). See also Strabo, lib. 16, ed. Almalov., vol. 2, p. 

 1125, B, 



