322 WHITE AND BLACK WATEHS. 



appear brown like coffee, or of a greenish black. These 

 waters, notwithstanding, are most beautiful, clear, and 

 agreeable to the taste. I have observed above, that the 

 crocodiles, and, if not the zancudos, at least the mos- 

 quitos, generally shun the black waters. The people 

 assert too, that these waters do not colour the rocks' ; and 

 that the white rivers have black borders, while the black 

 rivers have white. In fact, the shores of the Gruainia, known 

 to Europeans by the name of the Rio Negro, frequently 

 exhibit masses of quartz issuing from granite, and of a 

 dazzling whiteness. The waters of the Mataveni, when 

 examined in a glass, are pretty white ; those of the Atabapo 

 retain a slight tinge of yellowish-brown. "When the least 

 breath of wind agitates the surface of these ' black rivers' 

 they appear of a fine grass-green, like the lakes of Switzer- 

 land. In the shade, the Zama, the Atabapo, and the 

 G-uainia, are as dark as coffee-grounds. These phenomena 

 are so striking, that the Indians everywhere distinguish the 

 waters by the terms black and white. The former have 

 often served me for an artificial horizon; they reflect the 

 image of the stars with admirable clearness. 



The colour of the waters of springs, rivers, and lakes, 

 ranks among those physical problems which it is difficult, if 

 not impossible, to solve by direct experiments. The tints of 

 reflected light are generally very different from the tints of 

 transmitted light ; particularly when the transmission takes 

 place through a great portion of fluid. If there were no 

 absorption of rays, the transmitted light would be of a colour 

 corresponding with that of the reflected light ; and in general 

 we judge imperfectly of transmitted light, by filling with water 

 a shallow glass with a narrow aperture. In a river, the 

 colour of the reflected light comes to us always from the 

 interior strata of the fluid, and not from the upper stratum. 



Some celebrated naturalists, who have examined the purest 

 waters of the glaciers, and those which flow from mountains 

 covered with perpetual snow, where the earth is destitute of 

 the relics of vegetation, have thought that the proper colour 

 of water might be blue, or green. Nothing, in fact, proves, 

 that water is by nature white; and we must always admit 

 the presence of a colouring principle, when water viewed by 

 reflection is coloured. In the rivers that contain a colouring 



