RIVER, a current, or stream of fresh water, flowing in a bed or channel,from its source, into the sea. When a stream isnot large enough to bear boats, or small yes• sels 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 atig, mented 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 Da nube receives no less, before it enters the Euxine Sea. Some rivers are much ,aug mented 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 than 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 fill ed with water, and overflows its shelves and islands, though at other times of the year it is so shallow, as scarcely to af ford 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 de luges happen at different times of the year, because they proceed from various causes. Those that are swelled with rain are generally highest in winter, because it is usually then more frequent than at other times of the year; but if they pro.
teed from snow, which, in some places, is melted in the spring, in others, in sum mer, or between both, the deluges of the rivers 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, Varenius 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 se cure their grounds. Ile 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, &c. particularly in Guinea hi 1 river, where the negroes separate the gold-dust from the sand, and sell it to the Europe ans, who traffic thither fbr that very pur pose. 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 distinguish ed 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 ac count of the continual friction of the water against the bottom and sides of the chan nel, as well as from the various obsta cles they meet with in their progress, and from their arriving at length in plains, where the descent is less, and conse quently their inclination to the horizon greater.