322
W H I T E AND BLACK WATERS.
appear b r o w n like coffee, o r o f a greenish black. These waters, notwithstanding, are m o s t beautiful, clear, a n d agreeable t o the taste. I have observed a b o v e , that t h e c r o c o d i l e s , and, if n o t the z a n c u d o s , at least t h e m o s q u i t o s , generally shun the black waters. The people assert t o o , that these waters do not c o l o u r the r o c k s ; and t h a t the white rivers have black b o r d e r s , while the black rivers have white. I n fact, the shores o f the Guainia, k n o w n t o E u r o p e a n s b y the name o f the Rio N e g r o , frequently exhibit masses o f quartz issuing from granite, and o f a dazzling whiteness. T h e waters o f the Mataveni, when examined in a glass, are pretty w h i t e ; those o f the A t a b a p o retain a slight tinge o f y e l l o w i s h - b r o w n . W h e n the least breath o f wind agitates the surface o f these ‘black rivers’ they appear o f a fine grass-green, like the lakes o f Switzerland. I n the shade, the Z a m a , t h e A t a b a p o , and the Guainia, are as dark as coffee-grounds. These phenomena are so striking, that the Indians everywhere distinguish the waters by the t e r m s black and w h i t e . T h e f o r m e r have often served me for an artificial h o r i z o n ; they reflect the i m a g e o f the stars with admirable clearness. T h e colour of the waters o f springs, rivers, and lakes, ranks among those physical problems which it is difficult, if n o t impossible, to solve by direct, e x p e r i m e n t s . T h e tints o f reflected light are generally very different from t h e tints o f transmitted l i g h t ; particularly when the transmission takes place through a great portion of fluid. If there were n o absorption of rays, the transmitted light would be o f a c o l o u r c o r r e s p o n d i n g with that o f the reflected l i g h t ; and in general we judge imperfectly o f transmitted light, by filling with water a shallow glass with a narrow aperture. In a river, the c o l o u r o f the reflected light c o m e s t o u s always from the interior strata of the fluid, and n o t from the u p p e r stratum. Some celebrated naturalists, who have examined the purest waters o f the glaciers, and those which flow from mountains covered with perpetual snow, where the earth is destitute o f the relics o f vegetation, have t h o u g h t that the proper c o l o u r o f water might be blue, o r g r e e n . N o t h i n g , in fact, proves, that water is by nature w h i t e ; and wo must always admit the presence o f a c o l o u r i n g principle, w h e n water viewed by reduction is c o l o u r e d . I n the rivers that contain a c o l o u r i n g