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For when we see such great Rivers as the Rhine, the Elbe, &c. we more admire whence they proceed because

ceffarily meet with the high Ridges of Mountains that are difperfed over various Tracts of the Earth: each of which far furpaffes the ufual Height to which the Aqueous Vapours of themfelves afcend, and on the Tops of which the Air is fo cold, and rarified, as to retain but a small part of thofe Vapours that shall be brought thither by the Winds. The Vapours meeting with these Ridges of Mountains are there compelled by the Stream of the Air to mount up with it to their Tops, where meeting with more rarified Air, they naturally fall down in Drops, pervading the Crannies and Fiffures of the Earth, and gleeting into the Caverns of the Hills, the Water thereof gathers into the Bafons of Stone, or Clay, it finds, which being once filled, all the overplus of Water runs over, and, where it can find a Paffage, breaks out at the Sides of the Hills, and, forms Fountains; many of these, running down the Vallies, or Guts, between the Ridges of the Hills, and coming to unite, from Rivulets or Brooks; many of thele again being united into one common Chanel, form vaft large Rivers, as the Rhine, or the Danube.

This Theory of the Caufe of Springs the fame excellent Perfon proves by Experience. For he fays, that when he was in the land of St Helena, taking Aftronomical Obfervations in the Night-Time, on the Top of

the Hills about 800 Yards above the Sea, he found fuch a Condenfation of the Vapours, that in 7 or 8 Min. Time, tho' there was a clear Sky, the Glaffes of the Telescopes he used were covered with little Drops, and the Paper on which he wrote his Obfervationswould immediately be fo wet with the Dew that it would not bear Ink.

This Hypothefis he thinks more reafonable than that of those who derive all Springs from the Rain-Waters, which yet are perpetual and without Diminution, even when no Rain falls for a long Space of Time: Or than that which derives them from a Filtration or Percolation of the Sea Waters, thro' certain imaginary Tubes or Paffages within the Earth, wherein they lose their Saltnefs. This Opinion labours under this principal Abfurdity, that the greatest Rivers have their most copious Fountains farthest from the Sea, and where fo great quantities of fresh Water cannot reasonably be derived any other way than in Vapour. See Philof Tranf. No 192. Pag. 468.

Notwithstanding it is very probable that all Fountains have not the fame Origin; but that fome proceed from Rain penetrating the Fiffures of the Earth, and flowly gleeting thro' the Interftices to the Orifices of Springs; and others, especially those that are falt, and placed near the Sea Shore, take their Rife from the

Sea

because of the Quantity of their Water, than when we look upon fmall Brooks. But we have fhewed in the two laft Propofitions, that Rivers proceed partly from Rain and melted Snow, and partly from Lakes and Concurrences of Brooks and Rivulets; and therefore we do not enquire fo much here about the Sources of Rivers, as about the Origin and Permanency of Springs.

THE Opinions of Naturalifts and Geographers are various about this Matter.

1. SOME think that all Rivers and Springs receive their Water from Rain, or melted Snow; and this they bring for a Reason, that Rain and melted Snow fometimes augment Rivers to fuch a degree, that they overflow their Banks, and lay whole Countries under Water: But in the Summer Seafon, when no Rain has fallen for a long Time,

Sea Water percolating thro' the
Sands; but the greatelt part of
Fountains, efpecially fuch as
break from the fides of high
Hills, derive their Waters from
Vapours, as was said above.

The learned DrWoodward, in his Natural Hiftory of the Earth, explains the Origin of Fountains otherwise. He imagines, that there is a great Abyfs, or Promp tuary, of Waters, inclofed in the Bowels of the Earth, which, communicating with that of the Ocean, is continually exhaled into Vapours, by the Force of a fubterraneous Heat which he proves by many Arguments to be in the interior Parts of the Earth; and that as these make their way upwards, they pervade the Fiffures, and Intervals of the Strata of the Earth, permeating also the very Interstices of the Particles of Sand, Earth and

Stone, 'till they come near the Superficies of the Earth, where they are condenfed with cold, and come together by Drops, which, being collected, break out at fome Aperture or other, and form Fountains. But when the Heat above the Superficies of the Earth, is as intense as that in the interior Parts thereof, it takes the rifing Vapour, where it penetrates the Superficies of the Earth, and bears it up into the Air, or at least diminishes greatly.

They who would fee this Hypothefis more accurately explained, let them confult the learned Author in his Book: It is enough for us only to mention it, accounting Dr Halley's Theory much more clear, and built upon a better Foundation.

Jurin's Appendix. the

the great Rivers grow lefs, and the fmall ones are mostly dried up, because the Chanels of the later are too fhallow to contain any large quantity of Water; but the former, whofe Chanels are deep, do not ceafe running, nor are dried up, because they have collected fo much Water from the former Rain and melted Snow, that it cannot all be exhaled into Vapours, except it be by a lasting and conftant Heat. 2. Because there are the fewest Rivers where it feldom raineth, as in the inland Parts of Africa there are but few Springs.

BUT thefe Allegations do not folve the Propofition, which doth not enquire about the Origin of Rivers, but from whence the Water of Springs proceeds; therefore they that take this to be a Solution do not underftand the Sense of the Propofition, as we obferved before. And even the Property they propose to prove it by is not univerfal; for there are Rivers found in Places where they have feldom any Rain and no Snow, tho' what they fay is true concerning the Rivers in Egypt and Peru. Befide, Rain-Water doth not penetrate into the Ground beyond the depth of ten Foot; whereas feveral Fountains fpring from a greater Depth.

2. OTHERS think, that we are not to enquire about the Origin of the Water of Springs, fince it is an Element as well as the Earth, Air, and Fire, whofe Origins are not enquired into. This is Seneca's way of arguing. But thefe Authors cut the Gordian-knot when they cannot untie it; for we do not difpute about the Principles of Water, but enquire how it flows to the Heads of Rivers, rather than to any other Place. Moreover, the Earth is not a Fluid as Water is; and to fay, that the Air and Fire are not enquired into, is falfe. 3. THE Peripatetics follow the Opinion of their Mafter Ariftotle, delivered in Chapter xi.

Book i. de Meteor. where he endeavours to prove, that the Water of Springs is generated from Air contained in the Bowels of the Earth. These are his Reasons; 1. The Air, furrounding the Earth, is turned into Water, viz. into Rain; and therefore fince there is alfo Air in the Bowels of the Earth, and the fame Caufe to condenfe it, viz. Cold, it is contrary to Reafon to think that Water is not produced from Air there. 2. Experience teaches us, that great Drops gather from fmall ones under Ground, and therefore the Heads of Rivers are only a great many Springs gathered into one Place. For this Reafon, they that make Aqueducts, ufe to draw the Water thro' narrow Trenches and Pipes, which diftils, as it were, from the moift Earth, Drop by Drop. 3. Be cause most Fountains, efpecially of great Rivers, are found on mountainous Places, and but few upon Planes, it is a Sign that their Water proceeds from condenfed Air or Vapours, which naturally tend towards high Places; and Mountains are Sponges, as it were, lying upon the Planes. Thefe are Ariftotle's Reasons, to which this following may be added of no lefs Force than the reft, viz. that when the Air is clouded and filled with Vapours, acid Fountains tafte fweeter, which is a Sign they are augmented by the Air.

4. CARDAN and others are of Opinion, that the Water of Fountains proceeds from little Drains or Guts collecting the condensed watery Vapours both above and under Ground; but these seldom become Rivers, without being increafed with Rain and melted Snow. His Reasons are thefe; 1. If you obferve the Mountains in the Morning you will find them full of Moisture. 2. Rivers in the Morning are found to fwell, and the more the nearer they are to their Springs,

BUT

BUT the perpetual bubbling and springing up of the Water from Fountains, without any intermiffion, does not feem to be produced by fo weak and inconftant a Caufe. Neither is there much Difference between Ariftotle's Opinion and this of Cardan; only Ariftotle fays, Fountains proceed from Air condenfed, and Cardan, from Vapours; and there is but little Difference between Air and Vapours.

5. SOME of the Antients were of Opinion, that Rain-Water is hoarded up in the internal Caverns of the Earth, from whence it iffues, as out of a great Promptuary, and that all Rivers are fupplied from one common Fund, or spring one from another; alfo that no Water is difperfed over the Earth but fuch as is collected in the Winter Season, and reserved in thefe Receptacles, to be poured in due Time into innumerable Rivers: For this Cause, fay they, Rivers are greater in Winter than in Summer; and fome are perennial, others not. Their Reasons are the fame with those given for the firft Hypothefis. But Ariftotle and his followers reject this Opinion, because there is more Water poured out of the Mouth of one River in a Year, than the whole Bulk of the terraqueous Globe.

6. MANY of the modern Philofophers, with the Antients, fuppofe the Earth to fuck in as much Water as it exonerates into the Sea, thro' the Mouths of Rivers; and that the Sea-Water, by draining thro' the hidden Receffes of the Earth, and by being strained thro' the Mazes and Fiffures, and thro' the Interstices of the Sand and Gravel, lofeth it's Saltnefs, and becomes pure Water.

I am also of this Opinion, and think it most reafonable, but do not exclude the Caufes repeated in the firft and third Place. The Reasons for it are:

1. BECAUSE

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