GUPPOSED REASON OF THE COLOURS. 323 



principle, that principle is generally so little in quantity, thnt 

 it eludes all chemical research. The tints of the ocean seem 

 often to depend neither on the nature of the bottom, nor on 

 the reflection of the sky on the clouds. Sir Humphrey Davy 

 was of opinion that the tints of different seas may very 

 likely be owing to different proportions of iodine. 



On consulting the geographers of antiquity, we find that 

 the Greeks had noticed 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 of the Alps are sometimes of a 

 dark emerald 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 

 believed to be the purest; and it is rather from reasonings 

 founded on analogy, than from any direct analysis, that we 

 may throw any light on so uncertain a matter. In the vast 

 system of rivers near the mouth of the Bio Zama, a fact which 

 appears to me remarkable is, that the Hack waters are princi- 

 pally restricted to the equatorial regions. They begin about 

 five degrees of north latitude ; and abound thence to beyond 

 the equator as far as about two degrees of south latitude. The 

 mouth of the Eio Negro is indeed in the latitude of 3 9' ; 

 but in this interval the black and white waters are so singu- 

 larly mingled in the forests and the savannahs, that we 

 know not to what cause the coloration must be attributed. 

 The waters of the Cassiquiare, which fall into the Rio Negro, 

 are as white as those oi the Orinoco, from which it issues. 

 Of two tributary streams of the Cassiquiare very near each 

 other, the Siapa and the Pacimbny, one is white, the other 

 black. 



When the Indians are interrogated respecting the causes 

 of these strange colorations, they answer, as questions in 

 natural philosophy or physiology are sometimes answered in 

 Europe, oy repeating the fact in other terms. If you address 

 yourself to the missionaries, they reply, as if they had the 

 most convincing proofs of the fact, that " the waters are 

 coloured by washing the roots of the sarsaparilla." The 

 SmilacesB no doubt abound on the banks of the Rio Negro, 

 the Pacimony, and the Cababury ; their roots, macerated ir 



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