to the substances over or through which they pass. The purest of all waters we can any way obtain, is that distilled from snow, gathered in a clear, still, pinching night, in some very high place; taking none but the outer or superficial part of it. But a number of repeated distillations, the greatest part of the earth, and other feces, may be separated from this: and this is what we must be contented to call pure water. In a word, it is the opinion of Boerhaave, that no person ever saw a drop of pure water: that the utmost of its purity known, amounts only to its being free from this or that sort of matter; that it can never, for instance, be quite deprived of salt; since air will always accompany it, and air always contains salts. Many of the most eminent chemists have made experiments, in order to ascertain the conversion of water into earth. Boyle relates, that an ounce of water, distilled carefully in glass vessels two hundred times, yielded six drams of a white, light, insipid earth, fixed in the air, and indissoluble in water. Hence he concludes, that the whole water, by further prosecuting the operation, might be converted into earth. Godfrey, and others, concur in this opinion; but Boerhaave (who attributes the earth obtained by Boyle to the dust floating in the air, and to the instruments employed in the operation) is supported by Macquer, and others, in maintaining, that pure water is unalterable, and incapable of being decomposed; so that, whatever be the substances with which it is combined, when separated from these and sufficiently purified (and also when distilled singly, or mixed with other substances), its nature and essential properties still remain unchanged. Water seems to be diffused every where, and to be present in all space, where there is matter. There are few bodies in nature that will not yield. water; and it is even asserted, that fire itself is not without it. Among other remarkable circumstances, it has been observed, that bones dead and dried twenty-five years, and thus become almost as hard as iron, have yet, by distillation, afforded half their weight of water. Water is a very volatile body; it is entirely reduced into vapour, and dissipated, when exposed to the fire and unconfined. Heated in an open vessel, it has been observed to acquire no more than a certain determinate degree of heat, how intense soever the fire to which it is exposed; and this greatest degree of heat is that which it has at the moment before it begins to boil. It was formerly imagined, that water was incompressible, and therefore non-elastic; an opinion, founded on the famous Florentine experiment already mentioned, as proving its penetrative power. But the validity of the inferences drawn from this experiment have been justly questioned; Mr. Canton having proved, by very accurate experiments, that water actually is compressed by the weight of the atmosphere. But, not to be too diffusive on this subject, I shall endeavour to state concisely the nature of the component particles of water, and then its various uses. First: the particles of water are, as to our senses, infinitely small, whence their penetrative power. 2. Very smooth and slippery, or void of any sensible asperities. 3. Extremely solid. 4. Perfectly transparent, and as such invisible'. 5. If water be considered as consisting of spherical * Pure water, inclosed in a vessel hermetically sealed, projects no shadow, so that the eye cannot discover whether the vessel have water in it or not; besides, the crystals of salts, when the water is separated from them, lose their transparency. or cubical particles, hollow within-side, and of a firm texture, here will be enough to account for the difficulty of compressing it, and also for its being light, fluid, and volatile; its firmness and similarity will make it resist sufficiently; and its vacuity renders it light enough, &c. And the little contact between spherules (if, indeed, they touch at all) will account for the weakness of its cohesion. 6. Water is the most insipid of all bodies; the taste we sometimes observe therein not arising from the mere water, but from salt, vitriol, or other bodies mixed with it. And, lastly, it is perfectly inodorous, and void of the least smell. The uses of water are infinite; in food, medicine, agriculture, navigation, and many of the arts. As a food, it is one of the most universal drinks in the world; and, if we may credit many of our latest and most judicious physicians, it is also one of the best. As a medicine, it is found internally a powerful febrifuge; and excellent against colds, coughs, the stone, scurvy, &c. Externally, its effects are not less considerable. In agriculture and gardening, water is allowed absolutely necessary to vegetation. Many naturalists have even maintained it to be the vegetable matter, or the only proper food of plants; but Dr. Woodward has overturned that opinion, and en deavoured to show, that the office of water in vegetation is only to be a vehicle to a terrestrial matter, of which vegetables are formed, and that it does not itself make any addition to them. Water is of the utmost use in chemistry, being one of the great instruments by which all its operations are performed; and it is of the greatest service in many of the mechanical arts and ordinary occa sions of life. No. XVII. ON FOUNTAINS AND RIVERS. Addidit et fontes, immensaque stagna lacusque ; OVID. Fountains and ponds he adds, and lakes immense; WHAT a delightful ornament to a country is the winding course of a river! How much more exquisitely enchanting does it render the most beautiful landscape! And of what an unspeakable variety of benefits is it productive to the countries through which it flows! Hence rivers, in all their diversities of scenery, ever appear a favourite theme in poetical composition. Homer seldom mentions the country of any of his great personages, without introducing the principal river that waters it by some distinguishing characteristic. The Eridanus of the ancients (the modern Po) has been celebrated by Virgil, Claudian, and Lucan; Denham and Pope have immortalized the Thames ; and even the rivers in savage climes, that roll their immensity of waters through vast solitary wilds, have neither been neglected nor unsung by our de scriptive poets. When we contemplate a river at its fountain head, and perceive that, at first, it is nothing more than a little vein of water, oozing from some hil upon a bed of clay or sand, we naturally inquire into the causes of this phenomenon, or, in other words, into the origin of fountains and rivers. Concerning this subject natural philosophers have formed very different conjectures. Those, who imagine that fountains owe their origin to waters brought from the sea by subterranean ducts, give a tolerable account how they lose their saltness by percolation, as they pass through the earth: but they find great difficulty in explaining by what power the water rises above the level of the sea to the tops of mountains, where springs generally abound; it being contrary to the laws of hydrostatics, that a fluid should rise in a tube above the level of its surface. And Sir Richard Blackmore, in the first book of his poem entitled Creation, while he seems to admit this theory, thus inquires; Tell by what paths, what subterranean ways, Back to their springs the rivers to convey, } Des Cartes, in order to solve this difficulty, imagined, that after the water is become fresh by percolation, it is raised out of the caverns of the earth in vapours toward its surface; where meeting with rocks near the tops of mountains, in the form of arches or vaults, it adheres to them, and runs down their sides (like water in an alembic), till it meets with proper receptacles, from which it supples the fountains. Varenius and others imagine, that water may rise through the pores of |