fresh Water and we have fhewn that there is a different quantity of Salt in different Parts of the Sea; which must cause the Gravity of the Water to be unequal. But fome Sea-Water may happen to taste more falt than others, and yet be not more weighty; because it perhaps contains a greater quantity of volatile Salt, which does rather diminish than increase it's Weight, tho' it make it more falt. PROPOSITION XIII. Sea-Water doth not so easily freeze as fresh; or a greater Degree of cold is required to congeal Sea-Water, than to congeal fresh. EXPERIENCE fhews this, contrary to the Opinion of the Peripatetics, who mention that by how much Water is more pure, it is lefs liable to freeze, and that Sea-Water being more elementary than fresh will freeze the fooner; which is falfe. BUT the Caufe is, that in Salt there is a certain Spirit which refifts Coagulation, and this being feparated from it, will not congeal in the hardest Froft, as is well known to Chymifts: for they frequently make ufe of this Spirit of Salt (i). (i) The Particles of two different Bodies, which would be more at Reft when feparate, when they are mixed are put into new Motions by Attraction, which acts upon them only when they approach one another; and causes them to meet and clafh with great Violence, and to keep hot with the Mo tion. So that Water mixed with Salt, is more in Motion than Water alone; and therefore the Particles of Sea-Water are not fo eafily congealed, or made to reft, as the Particles of fresh, which do not refift the cold with fuch violent Motions. See Newton's Optics. Pag. 355. PRO PROPOSITION XIV. Why the Ocean is not enlarged when it receives fo many Rivers. THE Caufe is; 1. The Water returns from the Sea, thro' fubterraneous Fiffures to the Heads of the Rivers. 2. Plenty of Vapours are raised from the Ocean, a great Part of which being turned into Rain, fall partly into the Ocean, and partly on the dry Land (k). (4) Since the Ocean conftantly receives a prodigious quantity of Water, both from Rivers that exonerate themfelves into it, and alfo from the Air, in Dew, Rain, and Snow, that fall; it is impoffible but it fhould be enlarged, and encreafe to an immenfe Bulk, unlefs it be as much leffened fome other way. And seeing there hath not been obferved any fuch great increase in the Sea, and that the bounds of the Earth and Ocean are found to be in all Ages the fame, it remains that we inquire by what means the Ocean lofes fo much Water as it receives from Rain and Rivers flowing into it. There are two Hypotheses among Philofophers; one is, that the Water of the Sea is carried, by fubterraneous Conduits to the Springs of Rivers, and, in it's draining thro' the Fiffures, lofes it's Saltnefs: the other is, that it happens by the Vapours that are drawn up from it's Surface. The former is now re PRO jected by moft, it being difficult, if not impoffible, to explain how the Water of the Ocean, being more depreffed than the very Mouths of the Rivers, can come up to their Springs, which are, for the most part, on very high Mountains; but in the latter Hypothefis we have no Occafion to explain this, neither to hinder the Growth of the Ocean, nor to fupply the Springs with Water; both which may be more eafily done by the Vapours, which we certainly know to be drawn up from the Surface of the Sea. The quantity of Vapours drawn up from the Sea was tried by Dr Halley, who made the following Computation. Philof. Tranfact. N° 189. Page 366. By an Experiment made with great Care he found that Water, falted to the fame Degree as is common Sea-Water, and heated to the fame Degree of Heat, which is obferved to be that of Air in our hottest Sum mers, PROPOSITION XV. Some Parts of the Ocean differ in Colour from others. WE observe that towards the North Pole, the Sea feems to be of a black Colour, and in the Torrid Zone of a dufky Colour, and in other Places of a green Colour. Upon the Coaft of New Guinea, the mers, to exhale the thickness of a fixtieth Part of an Inch in two Hours. From whence it appears that a Bulk of Water a tenth Part of an Inch high will be exhaled into Vapours in twelve Hours. So that if the Superficies of the whole Ocean, or a Part of it, as the Mediterranean Sea be known, it may also be known how much Water arifes in Vapour from it every Day; fuppofing the Water to be equally hot with the Air in Summer. "For from what hath been "laid down, a Superficies of "ten fquare Inches emits daily "a cubic Inch of Water; "one fquare Foot, half a "Pint; Square whofe fides are 4 Feet, one Gallon; a fquare Mile, 6914 Tuns; "and one Degree fquare, (fup"pofed confifting of 69 Eng"lish Miles) 33 Millions of "Tuns." This learned Gentleman eftimates the Mediterranean to be about forty Degrees long, and four broad; allowances be ing made for the Places where it is broader by those where it is narrower, lo that it's whole Superficies may be accounted one hundred and fixty fquare Degrees; and confequently the whole Mediterranean muft lofe in Vapour, according to the foreftated Proportion, in a Summer's Day, at least five thoufand two hundred and eighty millions of Tuns. For what quantity of Water is licked off the Surface by the Winds, (which is even more fometimes than is exhaled by the Heat of the Sun) feems impoffible to be reduced to any Rule. It remains that we compare this quantity of Water with that which is carried daily into the Sea by the Rivers, which is very difficult to do, when we can neither measure the Breadth of the Chanels of these Rivers, nor the Velocity of the Currents. One thing is left, that a Comparison being made between these and the River Thames, and by fuppofing them rather greater than they are, we may have a greater quantity of Water than is really poured by them into the Mediterranean. The Mediterranean receives these nine confiderable Rivers; the Iberus, the Rhone, the Tiber, the the Sea in fome Parts appears white, and in others yellow: In Streights, or narrow Seas, it appears whitifh. Upon the Coast of Congo, not far from Baya d'Alvaro, where the fmall River Gonzales falls into the Sea, the Water is of a reddifh Colour which Tincture it receives from a red mineral Earth, thro' which the River flows. But the most famous for it's Colour is the Arabian Gulph, being therefore called the Red Sea. Some will have it to be only a bare Name, and taken from Erythrus, fome time King on that Coaft; others will have it to be called red from a certain Brightness peculiar to it, which is caused by the reflected Rays of the Sun (1). But the most probable Opinion, and which the Po, the Danube, the Neifter, the Borysthenes, the Tanais, and the Nile; all the reft being of no great Note. Each of these Rivers, this ingenious Gentleman supposes to be ten times greater than the Thames, not that any of them is fo great in Reality, but to comprehend with them all the fmall Rivulets that fall into the fame Sea. He supposes the River Thames, at Kingston Bridge, where the Flood feldom reaches to be in breadth about 100 Yards, and in depth 3; and the Water to run two Miles an Hour. If therefore the breadth of the Water, 100 Yards, be multiplied by 3, the depth, and the Product 300 fquare Yards by 48 Miles, or 84480 Yards, which the Water runs every Day, the product will be 25344000 cubic Yards of Water, or 20300000 Tuns that are carried every Day into the Sea. Now if each of the aforefaid mine Rivers yield ten times as much Water as the Thames; it will follow, that each of them carries every Day into the Sea 303 Millions of Tuns: and the whole nine, 1827 Millions of Tuns in a Day. But this is but little more than one third of what is proved to be raised, in Vapour, out of the Mediterranean in twelve Hours time. Hence it appears that the Mediterranean is fo far from increasing or overflowing by the Rivers running into it, that in a fhort Time it would rather be evaporated, and drawn out, unlefs the Vapours that it exhaled returned in Dew or Rain upon it. Jurin's Appendix. (1) Some will have this to be the fame with Esau or Edom, who firft inhabited Idumaa, a Country near the Arabian Gulph, from whence, fay they, it came to be called the Red-Sea, viz. from Edom, i. e. Red. SECT. IV. is confirmed by Experience, is, that it came to be fo called from the red Sand that lies upon the Shore, and is often contrary to it's Nature, mixed with the Water by the vehement Flux and Reflux of the Sea, which is extraordinary in this Gulph; infomuch, that it toffes it to and again like Afhes, and keeps it from falling to the Bottom by it's violent Agitation. This is related by Sailors, who tell us, that it fometimes appears as red as Blood; but if it be kept in a Veffel without fhaking, the red Sand will fubfide, and may be feen in the Bottom. very often happens, that violent Storms blowing from the Red-Sea, towards Arabia or Africa, carry with them fuch Heaps of red Sand, as to cover whole Caravans, or Troops of Men and Beasts, whofe Bodies in time are thus converted into true. Mummy. There are other Opinions among Authors, about the Name of this Gulph, but they are all of no Weight, as appears from Experience. It WHETHER the fame or fome other Caufe, hath urged Mariners to call the Gulph of California or (Vermejo) the Red-Sea, I have not yet found obferved by Authors. PROPOSITION XVI. There are certain Peculiarities obferved in fome Parts of the Ocean. THE Sea called by the Portuguese di Sargaffo, begins about the Salt Iflands, nor far from Cape Verd, and extends itfelf from the 20th Degr. of North Latitude, and to 34 Degr. South. It feems to be of a green Hue, tho' this be not it's proper Colour, but owing to a certain fmall leaved Herb, (not unlike Water-creffes) which we call the SeaLentile, or fmall leaved Parfley, but the Portuguese Sargaffo. The Leaves of this Weed are fo mutually |