RIVER. 
communication was kept up with the town 
by means of thejetie, which corresponded 
with the wooden bridge that joined the en- 
trance into the fort. The rampart was ca- 
pable of receiving forty-six pieces of ord- 
nance, which were disposed in three differ- 
ent alignements or tiers, owing to the tri- 
angular figure of the fort; so that a fire 
could be kept up on all sides. 
R'ITTERA, in botany, a genus of the 
Polyandria Monogynia class and order. 
Natural order of Leguminosse. Essential 
character : calyx four-leaved ; petals one, 
lateral ; legume one-celled, two-valved. 
There are five species. 
RIVER, a current, or stream of fresh 
water, flowing in a bed or channel, from 
its source into the sea. When a stream is 
not large enough to bear boats, or small 
vessels laden, it is called a rivulet or brook. 
The great, as well as the middle-sized rivers, 
proceed either from a confluence of brooks 
and rivulets, or from lakes ; but no river of 
considerable magnitude flows from one 
spring, or one lake, but is augmented by 
the accession of others. Thus the Wolga 
receives above two hundred rivers and 
brooks before it discharges itself into the 
Caspian Sea ; and the Danube receives no 
less, before it enters the Euxine Sea. Some 
rivers are much augmented by frequent 
rains, or melted snow. In the country of 
Peru and Chili, there are small rivers, that 
only flow in the day ; because they are only 
fed by the snow upon the mountains of the 
Andes, which is then melted by the heat of 
the sun. There are also several rivers upon 
both sides the extreme parts of Africa, and 
in India, which, for the same reason, are 
greater by day tlian by night. The rivers 
also in these places are almost dried up in 
summer, but swell and overflow their banks 
in winter, or in the wet season. Thus the 
Wolga in May and June is filled with water, 
and overflows its shelves and islands, though 
at other times of the year, it is so shallow, 
as scarcely to afford a passage for loaded 
ships. The Nile, the Ganges, the Indus, 
&c. are so much swelled with rain or 
melted snow, that they overflow their banks, 
and these deluges happen at different times 
of the year, because they proceed from 
various causes. Those that are swelled 
with rain are generally highest in win- 
ter, because it is usually then more fre- 
quent than at other times of the year ; but 
if they proceed from snow, which, in some 
places, is melted in the spring, in others, in 
summer, or between both, the deluges of 
the livers happen accordingly. Again, some 
rivers hide themselves under ground, and 
rise up in other places, as if they were new 
rivers. Thus the Tigris, meeting with 
mount Taurus, runs under it, and flows out 
at the other side of the mountain; also 
after it has run through the lake Tospia, 
it again immerges, and being carried about 
eighteen miles under ground, breaks out 
again, &c. The channels of rivers, except 
such as were formed at the creation, Vare- 
nius thinks, are artificial. His reasons are, 
that, when a new spring breaks out, the 
water does not make itself a channel, but 
spreads over the adjacent land; so that 
men were necessitated to cut a channel for 
it to secure their grounds. He adds, that 
a great number of channels of rivers are 
certainly known from history to have been 
dug by men. The water of most rivers 
flow impregnated with particles of metals, 
minerals, &c. Thus some rivers bring 
sands intermixed with grains of gold ; as in 
Japan, Peru, and Mexico, Africa, Cuba, 
ixc. particularly in Guinea is a river, where 
the negroes separate the gold-dust from the 
sand, and sell it to the Europeans, who 
traffic thither for that very purpose. The 
Rhine in many places is said to bring a 
gold mud. As to rivers that bring grains 
of silver, iron, copper, lead, &c. we find 
no mention of them in authors; though, 
doubtless, there are many, and it may be to 
them that mineral waters owe many of 
their medicinal virtues. 
Modern philosophers endeavour to re- 
duce the motion and flux of rivers to pre- 
cise laws ; and with this view they have 
applied geometry and mechanics to the 
subject ; so that the doctrine of rivers is 
become a part of the new philosophy. 
The authors, who have most distin- 
guished themselves in this branch, are the 
Italians, and among them more especially 
Gulielmini, and Ximenes. 
Rivers, says Gulielmini, usually have their 
sources in mountains or elevated grounds ; 
in the descent from which it is mostly that 
they acquire the velocity, or acceleration, 
which maintains their future current. In 
proportion as they advance further, this 
velocity diminishes, on account of the con- 
tinual friction of the water against the bot- 
tom and sides of the channel; as well as 
from the various obstacles they meet with 
in their progress, and from their arriving at 
length in plains where the descent is less, 
and consequently their inclination to the 
horizon greater. 
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