I.

CHAP. XVI.

Of RIVERS in general.

PROPOSITION I.

This Propofition contains fome neceffary Definitions.

A

RIVER is a Flux of Water continued thro' a long narrow Chanel, from one part` of the Earth to another. The Chanel is a Cavity, or hollow Place, made lower than the Banks, for the Water to run in.

2. A Brook is a little River, which is neither broad nor deep enough to carry a fmall Ship of Burden. A Navigable River is capable of carrying all forts of Ships, great and fmall; but thefe and the other fort are generally called great and small Rivers, according as they are in bignefs. A Torrent is a violent Flux of Water from the top of a Mountain.

3. A Confluence, Concurrence, or Conflux, is a Place where two Rivers meet.

4. BRANCHES of Rivers are the Brooks that run into them, and mix with them; or when a River is divided and runs in two Chanels, they are called it's Arms or Branches. Where the River is thus divided, it is called the Place of Parting or Divarication.

5. A Spring is the Place where running Water fprings out of the Ground. A Well is where the

Water rifes and runs not forward, but is kept upon the fpot.

PROPOSITION II.

Torrents and Brooks are fometimes generated from Plenty of Rain and melted Snow.

IN the elevated or mountainous Parts of the Earth, there are found many Receptacles, fmall Lakes, and Ponds, And when the Rain is poured into thefe, or the melted Snow, in fuch Quantity, that they are not large enough to contain it, they overflow and difcharge the fuperfluous Water into the under-land Places. This being done every Year, the Water in time makes itself a Chanel (tho' it fometimes flows without any certain Chanel). Thus a great many Torrents and Brooks, being fed only by Rain, or Snow melted from off the Mountains, before they have run their Course, become moderate Rivers; efpecially if they proceed from a long Range of Mountains; as thofe in the Foreland of Africa, India, Peru, Sumatra, &c. And what is remarkable, fuch Torrents flow in the Day-time only.

PROPOSITION III.

Most Rivers have their Rife from Springs.

THE great as well as the middle fized Rivers, proceed either from a Confluence or Collection of Brooks and Rivulets, or flow from Lakes and Moraffes. But no River of confiderable Magnitude (fuch as the Elbe, the Rhine, &c.) flows from one Spring or one Lake, but is augmented by the ae

2

ceffion

ceffion of others, flowing from other Fountains and Lakes. The Wolga or Rha receives above two hundred Rivers and Brooks, before it exonerates itfelf into the Caspian Sea; and the Danube receives no lefs, before it enters the Euxine Sea.

AND tho' Pliny and Cardan tell us, that no Rivers flow into the Nile, yet Experience fhews the contrary; as they that have travelled into Abyffinia affure us.

THIS Propofition may be proved by innumerable Examples.

THE Springs of Rivers are some of them found on the tops of Mountains, and fome on the Planes; and thofe Rivers that proceed from Lakes, have their Fountains (as was faid in the laft Chapter) at the bottom, or in the Chanel, of thofe Lakes that produce them, which like Cisterns contain the effufion of Water, 'till in a greater Quantity it be poured into it's proper Chanel. Hence fome Fountains are covered with Earth or Water, and others are open.

THE Springs of the Rivulets which begin the Tanais and the Elbe, are on Planes, to which others are afterwards joined. We might here add several Examples, but thefe are fufficient.

CARD AN is of Opinion, that these Fountains do not flow immediately from the Plane itself, but are conveyed by fubterraneous Aqueducts from the adjacent Mountains; however, I believe they first make a Lake or a Morafs; for the Tanais does not seem to flow immediately from a Spring, but from a Morafs or fhallow Lake.

THE Springs of moft Rivers are upon Mountains, as those of the Rhine, the Po, the Danube, the Niger, &c.

SEVERAL flow from Lakes, as the Nile, the Wolga, and the great River of St Lawrence in Canada.

A great

A great River may happen to flow from one Spring, if the Spring itself be fituated high (as moft are) and a great part of the Chanel low, or but a little higher than it's mouth; fo that the Water flowing with a fwift Course at firft, and by degrees flower, is increased in the Chanel and becomes a large River, because it discharges not fo much Water at it's mouth, as it received from it's Spring when it firft began to flow.

PROPOSITION IV.

Rivers are much augmented by frequent Rains or melted Snow, and at particular Times of the Year.

IN the Country of Peru and Chili there are fome Rivers fo fmall, that they do not flow in the Nighttime, but only in the Day; because they are fed by the Snow upon the Mountains of the Andes, which is then melted by the Heat of the Sun. There are alfo feveral Rivers upon both fides of the extream Parts of Africa, as in Congo, Angola, &c. which are greater by Day than by Night. The like are found both in Malabar and Cormandel in India. The Rivers alfo in thefe Places are almoft dried up in Summer, but fwell and overflow their Banks in Winter, or the wet Seafons. Thus the Wolga in May and June is filled with Water, and overflows it's Shelves and Iflands; which at any other time of the Year is fo fhallow, that it fcarcely affords a Paffage for loaded Ships. For the Snows being melted at this time of the Year, on the Mountains, from whence the Rivulets (being more than an hundred) flow into the Wolga, caufe this Inundation. The Nile, the Ganges, the Indus, &c. are fo much fwelled with Rain, or melted Snow, that, in like manner, they overflow their Banks. But these Deluges happen at divers times of the

Year,

Year, because they proceed from various Caufes and different Places. Thofe that are fwelled with Rains, are highest in Winter; because these are then more frequent than at other times of the Year; but if they proceed from Snow, which in fome Places is melted in the Spring, in others in Summer, or between both; the Deluges of the Rivers happen accordingly, viz. in the Spring, Summer, &c. or at the time when the Snow is melted upon the Banks of the Rivulets that form thefe Rivers. Moreover fome Rivers, especially the large ones, flow from Places at a great Distance, where it is Summer at the fame time it is Winter in the Places where they pass through; and for this Cause they overflow their Banks at different times of the Year. But most of them cause an Inundation in the Spring, because the Snow is then melted in moft Places. We fhall explain the Cause of their different Properties in the particular Description of each River.

WE fhall alfo in the next Chapter treat of that remarkable Spring in Japan, which only flows for two Hours every Day.

PROPOSITION V.

To explain the Origin of Springs (a).

THIS is easier to conceive than when it is propofed thus; From whence are Rivers generated?

(a) Since by Dr Halley's Calculation it appears, that the Vapours which are drawn up from the Sea exceed almoft three times the Quantity of Water difcharged into it by Rivers, [as was fhewn in the Note (k) upon Prop. xiv. Chap. xiii.] it will

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be no hard matter, feeing there is fuch an overplus of Water, to find enough from thence to fupply Fountains, according to the Opinion of the fame learned Gentleman.

For thefe Vapours being carried every way by theWind, neceffarily