a

my worthy friend to have

ble at a conjecture of mine, that fometimes the greater levity of water may depend on having a greater mixture of air. You fay you cannot conceive water having a greater or lefs mixture of air, water being an homogenous and fluid body, its parts, from the greatest to the leaft, being every where in fuch immediate contact as to leave no interftice or room for the admiffion of air.

This, dear Sir, is very far from being the cafe, the mixture or inclufion of air in water is evidently fhewn by the air-pump, where, any quantity of water being put, as the air contained within the machine is extracted, the water, with a kind of ebullition, throws up to the furface, in fmall bubbles, the air which it included. The caufe of this is, the ceffation of the preffure of the outward air, which before, bearing on the water, obstructed the expanfion of the air within; and by this operation all, or the far greater part, of the air, contained in the water is exhaufted, as appears from the ebullition ceafing at the conclufion of the experiment. But, fo difpofed is the water for the reception of new air, that, being again expofed, it admits a quantity of that element equal to what it had before, and even a greater quantity, if heated by the fire immediately before expofing it. This is manifefted by a repetition of the pneumatic experiment.

air when heated, is, that its pores are

The reafon of water admitting more

more open, and its particles more eafily divided.

But there is no need of recurring to the air-pump, for the investigation of this truth. Only expofe water in a glafs veffel, during a frosty night, you will, when frozen, fee in it fome small opake veficles, or whitish spaces. Did thefe fpaces, as all the reft, contain only frozen water, there would be no more colour nor opakeness in them than in the reft. What then is their contents? Some aggregated portions of air; for the water being more compreffed by the cold, feveral particles of air, difperfed in it, formed those spaces vacant; fo as, by virtue of its elafticity, to acquire a greater extenfion than before; and this accounts for water, when frozen, occupying a greater fpace, than when in its natural state of liquidity. This, however, is to be underftood of the whole volume, compounded of air and water; for, ftrictly fpeaking, the frozen water alone does in reality take up lefs fpace than before. Here my friend may wonder how those bubbles, containing only air, which is more tranfparent than water, fhould appear opake: but it is a conftant law in dioptrics, that light is lefs tranfmitted through two mediums of an unequal transparency, than through only a fingle medium, though lefs tranfparent than either. For a conviction

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of this, only look on a piece of coarfe glafs, and you'll find in it many fmall opake spaces, which are owing only to fome portion of air intercepted in them, at the time of making. If this be not fatisfactory, break a piece of fuch glafs into feveral bits, and in thofe opake spaces you'll find it to be hollow.

You now see, Sir, that all the particles of water are not every where in mutual contact, as you imagined, and on which you grounded your denial of air being contained in it; but you have fomething farther to fee, and I now call your attention to what will appear a fhocking paradox, and yet will force your belief. So far are the particles of water from leaving no void interftice between them, I aver, that the void spaces between them are fuch as to take up above eighteen times a greater space than the water itself; fo that, in a veffel which, to outward appearance, seems full of water, the water does not occupy fo much as the eighteenth part of its capacity; the void spaces intercepted in the water itself form a volume above eighteen times larger than that of the very fubftance of the liquor. Here you ask me with what eyes I saw thofe fpaces?-With the eyes of reafon; and thus I prove it.

All philofophers agree, and, what is more, it is demonftrated, that the weight of bodies is proportionate to their dentity. The molt dense body is moft heavy, and the most rare is leaft fo; and they more and the lefs precisely conform to the degrees of denfity; that is, a body twice as denfe as another is twice as heavy; if at four times the density, four times the fpecific weight. What do you mean by one body's being more denfe than another? The containing more of its proper matter in an equal volume. For inftance, a piece of oak is three times as heavy as another of fir of equal bignefs, because it is three times as denfe, that is, it contains within equal dimenfions three times more of its proper fubftance than that of fir; or, which amounts to the fame, the latter is thrice as porous or has three times the void interftices as the former; for what fills the pores in the wood, be it air or any thing else, is

adventitious, and not the proper fubftance of the timber.

Farther, gold is known to be nine. teen times fpecifically heavier than water, and the excess of denfity being as that of weight, gold contains in an equal volume nineteen times more of proper fubitance than water; so that in a cubic foot of gold nineteen parts are of the natural substance, whereas in a like volume of water there is only one. Water, on the other hand, is fo rare, that in a cubic foot, its proper-fubftance, even at most, takes up only a nineteenth part, all the remainder being occupied by the air or fubtile matter within the numberless void pores or interftices in the water.

A nineteenth part did I fay? not fo much, or rather much lefs. Were gold fo denfe as to exclude all porofity, a comparison of its weight with that of water would only prove that the latter fills the nineteenth part of the fpace, and no more. But gold, being likewife not without pores, and confe quently its proper fubftance not taking up the whole fpace, i. e. of the cubic foot, the refult of comparing the weight is, that the porofity of the water is greater than eighteen parts of the space. For inftance, if the fubftance of the gold, by reafon of its porofity, occupies only two parts of the fpaces, leaving the third for the air or fubtle matter within its pores, then is the porofity of water one third more thu what takes up eighteen parts of the fpace, confequently the matter contained within its pores will occupy twenty-fix parts of the space, and the proper fubftance of the water only a twenty-feventh part.

Gold porous! will fome fay; yes, doubtless and fo porous, that the point of the finest needle cannot indicate any part of a piece of gold free from porofity. A proof of this is the diffolution of gold by aqua regia, for how could that liquor diffolve gold but by pervading its pores? Another proof of this porofity is to be met with in Oranam's Recreations Mathematiques, tom. 3. One end of an ingot of gold being put into mercury, it penetrates the other fide, the mercury meeting every where with voids or ducts through