SUPPOSED SEASON OP THE COLOUES. 
323 
principle, that principle is generally so little in quantity, that 
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 
'yas of opinion that the tints of different seas may very 
likely he owing to different proportions of iodine. 
On consulting the geographers of antiquity, we find that 
the Greeks had noticed the blue waters of Thermopyl®, the 
r ed waters of J oppa, and the black waters of the hot-baths 
. Nstyra, opposite Lesbos. Some rivers, the Bhone for 
instance, near Geneva, have a decidedly blue colour. It is 
said, that the snow-waters of the Alps are sometimes of a 
hark 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 
elieved to be the purest; and it is rather from reasonings 
rounded on analogy, than from any direct analysis, that we 
lay throw. any light on so uncertain a matter. In the vast 
system of rivers near the mouth of the Eio Zama, a fact which 
a Ppears to me remarkable is, that the blacJc waters are princi- 
pally restricted to the equatorial regions. They begin about 
hve degrees of north latitude ; and abound thence to beyond 
he equator as far as about two degrees of south latitude. The 
jhouth of the Bio Negro is indeed in the latitude of 3° 9' ; 
,° u * in this interval the black and white waters are so singu- 
a rly mingled in the forests and the savannahs, that we 
«now not to what cause the coloration must be attributed. 
,' he waters of the Cassiquiare, which fall into the Eio Negro, 
0? as white as those ot the Orinoco, from which it issues! 
o t two tributary streams of the Cassiquiare very near each 
hlack tlle S ‘ a P a ancl tlle Phuimony, one is white, the other 
of^vi^ 611 ^ ie ■friihhns are interrogated respecting the causes 
Hat C ? e s i ran g e colorations, they answer, as questions in 
j, oral philosophy' or physiology are sometimes answered in 
y Q °P®> ’ 5 y repeating the fact in other terms. If you address 
. ^! e missionaries, they reply, as if they had the 
coin C j n ™™g proofs of the fact, that “ the waters are 
S ' lred hy washing the roots of the sarsaparilla.” The 
the p C< -° 110 abound on the banks of the Bio Negro, 
-l acimony, and the Cababury ; their roots, macerated in 
