times fee all the fish of a pond killed, when the ice every where covers the furface of the water; and thus keeps off the air from the fubjacent fluid. If a hole be made in the ice, the fifh will be seen to come all to that part, in order to take the benefit of a fresh fupply. Should a carp, in a large vafe of water, be placed under an air-pump and then be deprived of its air, during the operation a number of bubbles will be feen ftanding upon the furface of the fifh's body; foon after the animal will appear to breathe fwifter and with greater difficulty: it will then be feen to rife towards the furface to get more air; the bubbles on its furface begin to disappear; the belly, that was before fwollen, will then fall of a fudden, and the animal finks expiring and convulfed at the bottom. So very neceffary is air to all animals, but particularly to fifh, that, as was faid, they can live but a few minutes without it: yet nothing is more difficult to be accounted for, than the manner in which they obtain this neceflary fupply. Those who have feen a fifh in the water, muft remember the motion of its lips and its gills, or at least of the bones on each fide that cover them. This motion in the animal is, without doubt, analogous to our breathing, but it is not air, but water, that the fish actually fucks in and spouts out through the gills at every motion. The manner of its breathing is thus: the fish first takes a quantity of water by the mouth, which is driven to the gills; thefe clofe and keep the water fo fwallowed from returning by the mouth; while the bony covering of the gills prevents it from going through them, until the animal has drawn the proper quantity of air from the body of water thus imprisoned: then the bony covers open and give it a free paffage; by which means alfo the gills again are opened and admit a fresh quantity of water. Should the fish be prevented from the free play of its gills, or fhould the bony covers be kept from moving, by a ftring tied round them, the animal would foon fall into convulfions and die in a few minutes. But though this be the general method of explaining refpiration in fishes, the difficulty remains to know what is done with this air, which the fish in this manner feparates from the water. There feems no receptacle for containing it; the ftomach being the chief cavity within the body, is too much filled with aliment for that purpose. There is indeed a cavity, and that a pretty large one, I mean the air-bladder or fwim, which may ferve to contain it for vital purposes; but that our philofophers have long deftined to a very different ufe. The ufe univerfally affigned to the airbladder is the enabling the fish to rife or fink in the water at pleasure, as that is dilated or comprefied. The ufe affigned by the ancients for it was to come in aid of the lungs, and to remain as a kind of store-house of air to fupply the animal in its neceflities. I own my attachment to this laft opinion; but let us exhibit both with their proper fhare of evidence, and the reader must be left to determine. The air-bladder is described as a bag filled with air, fometimes compofed of one, fometimes of two, and fometimes of three divifions, fituated towards the back of the fish, and opening into the maw or the gullet. Thofe who contend that this bag is defigned for raifing or depreffing the fish in the water, build upon the following experiment. A carp being put into the pump and the air exhaufted, the bladder is said to expand itself to fuch a degree, that the fifh fwells in an extraordinary manner till the bladder burfts, and then the fish finks,and ever after continues to crawl at the bottom. On another occafion, the air-bladder was pricked and wounded, wounded, which let out its air; upon which the fifh funk to the bottom, and was not feen to rife after. From thence it is inferred that the use of the air-bladder must be by fwelling at the will of the animal, thus to encrease the furface of the fifh's body, and thence diminishing its specific gravity, to enable it to rife to the top of the water, and keep there at pleafure. On the contrary, when the fish wants to defcend, it is, fay they, but to exhaust this bladder of its air; and the fish being thus rendered flimmer and heavier, confequently finks to the bottom. the air-bladder, according to their hypothefis, to iwell under the experiment of the air-pump? What is it that clofes the aperture of that organ in fuch a manner as at laft to burst it; or what neceffity has the fish for dilating it to that violent degree? At moft, it only wants to rife to the furface; and that the fish can eafily do without fo great a diftention of the air-bladder. Indeed, it fhould rather feem, that the more the air was wanted without, the lefs neccility there was for its being ufelefsly accumulated within; and to make the modern fyftem confiftent, the fish under the air-pump, inflead of permitting its bladder to burft, would readily give up its contents; which, upon their fuppofition, all can do at pleafure. the gullet; and what air is put into it muft remain there till the neceffities, and not the will, of the animal call it forth as a fupply. Such is the account given of the ufe of the air-bladder; no part of which feems to me well fupported. In the first place, though nothing is more certain, than that a carp put into the air-pump will fwell, yet fo will But the truth is, the fifh can neia moufe or a frog; and thefe we ther increafe nor diminish the quanknow have no air-bladders. A carp tity of air in its air-bladder at will, will rife to the furface; but fo will no more than we can that which is all fish that want air, whether they contained in our ftomachs. The ahave an air-bladder or not. The air- nimal has no one muscle, much less bladder is faid to burst in the expe- pair of mufcles for contracting or diriment; but that I deny. The air-lating this organ; its aperture is from bladder is indeed found empty, but it has fuffered no laceration, and may be diftended by being blown into like any other bladder that is found. The fifh after the experiment, I grant, continues to creep at the bottom; and fo will all fifh that are fick and wounded, which must be the cafe with this after fuch an operation. Thus thefe facts prove nothing, but that when the fish is killed in an airpump, the air-bladder is found exhaufted; and that it will naturally and neceffarily be; for the drain of air by which the fifh is fupplied in the natural way will neceffarily oblige it to make ufe of all its hidden flores; and, as there is a communication between the gullet and the airbladder, the air which the latter contains will thus be obviously drawn away. But ftill farther, how comes But, to put the matter paft a doubt, many fifh are furnished with an airbladder that continually crawl at the bottom; fuch as the cel and the flounder; and many more are entirely without any bladder, that fwim at eafe in every depth; fuch as the anchovy and fresh water gudgeon [Redi]. Indeed, the number of fish that want this organ is alone a fufficient proof that it is not fo neceffary for the purpofes of fwimming: and as the ventral fins, which in all fish lie flat upon the water, feem fully fufficient to keep them at all depths, I fee no great occafion for this internal philofophical apparatus for raifing and depreffing them. Upon the whole, the air bladder bladder feems adapted for different purposes than that of keeping the fifh at different depths in the water; but whether it be to fupply them with air when it is wanted from without, or for what other purpose, I will not take upon me to determine. (To be concluded next month.) On the NATURE and PROPERTIES of WATER. IT Nymphs! your bright squadrons watch with chemic eyes The cold elaftic vapours, as they rife; With playful force arreft them as they pass, T was the opinion of Thales, and other ancient philofophers, that Water was the original of all things. Hence Pindar, when he would illuftrate the fuperiority of the Olympic games over all others, fets out with obferving, that they hold the fame rank as Water docs among the elements, and gold among the gifts of Fortune. Chief of Nature's works divine Water claims the highest praife, Richeft offspring of the mine, Gold like fire, whofe flashing rays, From afar confpicuous gleam Thro' the night's involving cloud, Firft in luftre and esteem, Decks the treasures of the proud; So among the lifts of fame Pifa's honour'd games excel; Then to Pifa's glorious name Tune, O Mufe, thy founding fhell. WEST'S PINDAR. Nor was this opinion confined to remote antiquity. Van Helmont, and others among the moderns, have likewife maintained, that Water is the clemental matter, or ftamen, of all BOTANIC GARDEN, Part I. things, and is alone fufficient for the production of all the vifible creation. And fir Ifaac Newton thus expreffes himself on this fubject: All birds, beafts, and fishes, infects, trees, and vegetables, with their feveral parts, do grow out of water,and watery tinc tures and falts; and, by putrefaction, they all return again to watery fubftances.' The fame great philofopher defines Water to be a fluid salt, volatile, and void of tafte. But Boerhaave fets afide this definition; for Water,' he obferves, is a menftruum, or diffolvent of falts and faline bodies, which does not agree with the notion of its being a falt itfelf; for we do not know of any one falt that diffolves another.'-By fome late experiments of Lavoifier, Watt, Cavendish, Priestley, and Kirwan, it appears, that Water confifts of dephlogifticated air, and inflammable air or phlogifton intimately united; or, as Mr. Watt conceives, of dephlogifticated air and phlogiston, deprived of part of their latent heat. This doctrine is alluded to in my motto.* In * Until very lately water was efteemed a fimple element, zor are all the moß celebrated chemifts of Europe yet converts to the new opinion of its decompofition. Mr. Lavoifier and others of the French school have most ingeniously endeavoured In contemplating Nature, we fhall often find the fame fubftances poffeffed of contrary qualities, and producing oppofite effects. Air, which liquifies one fubitance, dries up another. That fire which is feen to burn up the defert, is often found, in other places, to affift the luxuriance of vegetation; and Water, which, next to fire, is the most fluid fubftance upon earth, gives to all other bodies their firmness and durability: fo that every element feems to be a powerful fervant, capable of either good or ill, and only awaiting external direction, to become the friend or enemy of mankind. Thefe oppofite qualities, in Water in particular, have not failed to excite the admiration and enquiry of the curious. That Water is the most penetrating body next to fire, and the most difficult to confine, has been proved by various experiments. A veffel through which water cannot pafs, may retain any thing. Nor is it any objection, that fyrups and oils will fometimes pass through bodies which hold Water; this not being owing to the greater fubtility and penetrability of their particles, but to the refia with which the wood of fuch veffels abounds, and to which oils and fyrups are as menftruums; fo that, diffolv ing the refin, they make their way through the fpaces left thereby. But Water, on the contrary, not acting on refins, is retained in the fame vefiels. And yet it gradually makes its way, even through all woods, and is retainable only in glafs and metals. It was found, moreover, by an experiment at Florence, that when fhut up in a fpherical veffel of gold, and then preffed with great force, it made its way through the pores even of the gold: fo that the moft folid body in nature is permeable to Water, under certain circumftances. It is even found more fluid than air; a body being reputed more fluid than another, when its parts will find way through fmaller pores. Now air, it is well known, will not pafs through leather; as is evident in the cafe of an exhausted receiver covered therewith; but Water will pafs through leather with eafe. Air, likewife, may be retained in a bladder, which Water oozes through. It is found, indeed, that Water will pafs through pores ten times fmaller than air will.-But here it must be obferved, that M. Homberg accounts for this paffage of Water through the narrow pores of animal fubftances, which will not admit the air, on the principle of its moiftening and diffolving the gluti nous to fhew that water confifts of pure air, called by them oxygene, and of infiammable air, called hydrogene, with as much of the matter of heat, or calorique, as is neceffary to preferve them in the form of gas. Gas is diftinguished from feam by its preferving its elafticity under the preffure of the atmosphere, and in the greatest degrees of cold yet known. The hiftory of the progress of this great difcovery is detailed in the memoirs of the Royal Academy for 1781, and the experimental proofs of it are delivered in Lavofier's Elements of Chemistry. The refults of which are that water confifts of 85 parts by weight of oxygene, and 15 parts by weight of hydrogene, with a fufficient quantity of calorique. Not only numerous chemical phenomena, but many atmospherical and vegetable facts, receive clear and beautiful elucidation from this important analyfis. In the atmosphere inflammable air is probably perpetually uniting with vital air and producing moisture which defcends in dews and fhowers, while the growth of vegetables by the affiftance of light is perpetually again decompofing the water they imbibe from the earth, and while they retain the inflammable air for the formation of oils, wax, honey, refin, &c they give up the vital air to replenish the atmosphere. Botanic Garden, Part I. page 132. nous matter of the fine fibres of the membranes,and rendering them more pliable and diftractile; which is what the air, for want of a wetting quality, cannot do. As a proof of this doctrine he filled a bladder, compreffed it with a ftone, and found no air to come out; but placing the bladder, thus compreffed, in water, the air eafily escaped. Hence Water, from it penetrative power, may be fuppofed to enter into the compofition of all bodies; vegetable, animal, and fofil; with this particular circumftance, that it can always be separated, by a gentle heat, from thofe fubftances with which it has been united. Fire, indeed, will penetrate more than Water; but it is not fo eafily to be feparated again. This property of Water, joined with its fmoothness and lubricity, fits it to ferve as a vehicle for the commodious and easy conveyance of the nutritious matter of all bodies. Being fo fluid, and paffing and repaffing fo readily, it never ftops up the pores, and leaves room for the following Water to bring on a new fupply of nutritious matter. The fame Water, however, fo little cohefive as it is, and fo cafily to be feparated from moft bodies, will cohere firmly with fome others, and bind them together in the moft folid maffes; though it appears wonderful, that Water, which may be fhewn an almost univerfal diffolvent, fhould, nevertheless, be a great coagulator. Water, mixed up with earth and afhes, gives them the utmolt firmness and fixity. The afhes, for inftance, of an animal, incorporated with pure Water into a paste, and baked with a vehement fire, become a copple; which is a body remarkable for this, that it will bear the utmost effort of a refiner's furnace. It is, in reality, upon the glutinous nature of Water only, that our houfes ftand: for take the Water out of wood, and it be comes afhes; or out of tiles, and they become duft. A little clay, dried in the fun, becomes a powder, which, mixed with Water, flicks together again, and may be fafhioned to any form; and this, dried again by a gentle fire, or in the fun, and then baked in a potter's oven by an intense fire, becomes little other than a ftone. The Chinefe earth, of which our porcelain veffels are made, which hold all liquors, and even melted lead itself, is diluted and wrought up with Water. In fine, all the ftability and firmnefs vifible in the univerfe have been afcribed, by fome writers, to Water alone. Thus, they fay, ftone would be an incoherent fand, did not Water bind it together; and thus, again, of a fat, gravelly earth, wrought up with Water, and baked, or burnt, we make bricks, tiles, and earthen vessels, of fuch exceeding hardness and closenefs, that Water itself cannot pafs through them. And thefe bodies, although to appearance perfectly dry, and deftitute of Water,yet,being pulverized, and put into a retort, and diftilled, yield an incredible quantity of Water. The fame, it is faid, holds of metals; for the parings or filings of lead, tin, antimony, &c. yield water plentifully,by diftillation; and the hardeft ftones, fea-falt, nitre, vitriol, fulphur, &c. are found to confift chiefly of Water, into which they refolve by the force of fire. The lapis calcarius, or lime-stone, being expofed to the fire, affords a prodigious quantity of pure Water; and the more of this Water is extracted, the more friable does it become, till, at length, it commences a dry calx, or lime, wherein, in lieu of the Water fo expelled, the fire enters, in the courfe of calcination; and this is expelled again, in its turn, by pouring on cold Water. Yet the fame Water and calx, tempered together, produce a mafs, fcarce inferior, in point of folidity, |