are really made of copper and tin; ftatuary-metal is much of the fame kind; and bell-metal differs only in having a larger proportion of tin, or fometimes a little zinc. The tin is chiefly added to make the copper melt more eafily; but it has another advantage in making ordnance, that of rendering the piece lighter. Perhaps lead, as lefs fonorous, might leffen the fharp tone of the explosion. At York Town, when lord Cornwallis's army furrendered, the French cannon were distinguished by the acutenefs of their found, and were called by our men, from the found, and the impreffion the balls made on the new works, fharp-fhakes. We have been informed that the French add zinc, inftead of tin, in making their brafs cannon. The continental currency, coined by congrefs in 1776, is now faid to have become fcarce: the bishop fufpects that it confifts of twelve parts of tin, and one of lead. The beft fpeculum metal is made with fourteen ounces and a half of grain tin, and two pounds of copper. The excellence of Mr. Mudge's method of re-melting the compofition, to avoid pores, in Dr. Watfon's opinion, arifes from the metal being in thinner fufion. In cafting fleel, a bar, from this caufe, will be one inch in thirty-fix fhorter than another, cast when the metal was not equally fluid; and this laft will be found to have many pores or blebs.

It may deferve to be remarked, and I fhall have no other opportunity of doing it, that the melting or cafting of fteel was introduced at Sheffield, about forty years ago, by one Waller from London, and was afterwards much practifed by one Huntsman, from whom fteel fo prepared, acquired the name of Huntiman's caft fteel. It was at first fold for fourteen pence, but may now be had for ten pence a pound; it cofts three pence a pound in being melted, and for drawing ingots of caft feel into bars of the fize of rafors, they pay only fix fhillings for a hundred weight, and ten fhillings for the fame quantity when they make the bars into a fize fit for small files, &c. The caft fteel will not bear more than a red heat; in a welding heat it runs away under the hammer like fand. Before the art of cafting fteel was introduced at Sheffield, all the caft fteel ufed in the kingdom was brought from Germany; the bufinefs is carried on at Sheffield with greater advantage than at most other places, for their manufactures furnish them with great abundance of broken tools, and thefe bits of old steel they purchase at a penny a pound and melt them, and on that account they can afford their caft fteel cheaper than where it is made altogether from fresh bars of steel.'

The next Effay is on Tinning Copper, on Tin and Pewter. The account which foreigners have given of our tin arises, in Dr. Watson's opinion, from their having, instead of it, ex

Common

amined pewter, which has fometimes this name. block-tin is faid to contain neither lead, antimony, or copper; but, when pure, its fpecific gravity is much below the point at which it is ufually eftimated. Dr. Watfon makes it only 7170, so that other authors feem to have employed an adulterated metal. The compofition of different kinds of pewter is next defcribed; but this fubject is commonly underfood. Tinning copper was, in our author's opinion, an ancient practice. In France, zinc has lately been used for this purpose, and the coat is put on 'iron veffels. In our way, lefs than a grain of tin is fpread on a square inch; but, by a discovery lately made at Paris, twenty times as much readily adheres to the fame furface of copper. This fubjec will still admit of improvement: we remember once to have feen the specification of a patent for a new method of tinning, in which the coat was faid to laft as long as the veffel. It confifted in making many minute holes in the copper, and melting the tin on it; but the inventor ought to have said, that the veffel would laft no longer than the coat. In a very little time both were ufelefs.

The fifth Effay is on Tinning Iron.-Of Plating and Gilding Copper. The author gives fome curious particulars of the hiftory and method of making tinned iron plates, and the following hint, at leaft, deferves notice.

Tin is not, but iron is liable to contract ruft by exposure to air and moisture, and hence the chief use of tinning iron is to hinder it from becoming rufty; and it is a queftion of fomet importance, whether iron of a greater thickness than the plates we have been speaking of, might not be advantageously tinned. I defired a workman to break off the end of a large pair of pincers, which had been long used in taking the plates out of the melted tin; the iron of the pincers feemed to have been penetrated through its whole fubflance by the tin; it was of a white colour, and had preferved its malleability. It is ufual to cover iron ftirrups, buckles, and bridle bits, with a coat of tin, by dipping them, after they are made, into melted tin; and pins, which are made of copper wire, are whitened, by being boiled for a long time with granulated tin, in a lie made of alum and tartar. Would the iron bolts, ufed in fhip-building, be preferved from rufling, by being long boiled in melted tin P

The different methods of plating and gilding copper are then fhortly, and we believe accurately delineated.

The next Effay is on Gilding in Or Moulu, that is, with gold diffolved by quickfilver. This fubject introduces the ufe of quickfilver in feparating the richer metals, viz. gold and filver from earths. The author, in this part of his Effay, mentions the very numerous diftillations of the fame quick

filver by Boerhaave; its long digeftion, and conftant agitation in a fulling-mill, without any other change than producing a black powder, which, by trituration in a mortar, again became running mercury. Dr. Watfon concludes, by defcribing the combinations of tin and mercury, and their application in making looking glaffes. A curious and entertaining history of this invention is fubjoined, in which many new facts are adduced, and its antiquity extended beyond our expectations.

The tranfmutability of Water into Earth is then examined, and the best arguments, and moft decifive experiments of the different combatants on this question, are accurately adduced. Dr. Watson seems to think that the water is really changed; but we are now arrived much nearer to a conclufion; and we fhall not anticipate what we may have foon occafion to enlarge on,

The laft Effay is on Westmoreland Slate, and various Sorts of Stone in it, Dr. Watson compares the advantages of all the different kinds of covering on houses; but this fubject would detain us too long. The following fact we shall tranfcribe, fince it feems ufeful, and may be very important.

• We have a stone which is of a calcareous nature, and is called clunch, in this neighbourhood; it is foft and easily wrought, and when properly placed in a building is very durable; but if the pofition of the ftone in the building be differ ent from what it was in the quarry, that is, if the fide of the ftone which in the quarry was parallel to the horizon, be either perpendicular, or inclined to it, in the building, it foon cracks and moulders away; and I am not certain but the durability of Portland ftone itself, may have fome dependence on its pofition in a building, being fimilar to, or diflimilar from that, which it had in the quarry; and this may be one reason why we fee in Blackfriars Bridge, and in fome houses and other edifices in London, which are made of Portland stone, a few ftones which are more decayed than the rest.'

Some remarks on Foffil Glafs (Pliny's lapis obfidianus), which Dr. Watson thinks may have been found in old volcanos, obfervations on different kinds of ftone, with their feveral fpecific gravities, are next fubjoined. The Guernsey granite is exceedingly heavy; and, as it contains fo much matter in a fmall bulk, is fuppofed to make the most durable pavement. The fpecimens, in our poffeffion, have a ftill greater specific gravity, though the excefs is fo flight as not to deserve notice, The ftone from which they were struck, refifted, however, the strongest blow, on the thinneft edges, with a heavy iron mallet, and repelled it with a very acute found.

We shall felect the bishop's conclufion. It is an animated and juft peroration, perfectly confiftent with epifcopal de

corum,'

corum,' and well adapted to the object and defign of these volumes.

The analyzing the various ftones which are met with, either in large beds in the earth, or in detached pieces at the bottoms of the rivers, or on the fea coafts of the kingdom; and the lodging the fpecimens in fome public receptacle, where they might be feen by the ftudents in natural history, might Occupy very usefully the leifure of a philofophical chemift. He would find a far greater variety of jafpers, porphyries, granites, flints, limestones, flates, lavas, &c. than at the firft view of the fubject he would probably expect. Experimental inveftigations of this fort, made with ability and caution, in different parts of the world, are the only fure foundations on which we can ever hope to build any probable fyftem concerning the formation of mountains, the antiquity of the present form of the globe, and the caufes of the viciffitudes which it has undergone. It is the proper province of natural philofophy to explore fecondary caufes; they are the fteps on which the mind of man afcends from earth to heaven: for the more distinctly we apprehend the number and connexion of the fecondary caufes operating in this little fyftem which is fubmitted to our view, the more certainly fhall we perceive the neceffity of their ultimately depending, like the links of Homer's chain, on a firft.'

To repeat our commendations would be improper; to add to them, unneceffary: our regret at being precluded from this kind of inftructive entertainment, we have already expreffed. We must leave our author then, with reluctance leave him, expreffing our wishes that his future pursuits may be as fuccefsful as his former ones; they need not be more so!

A Differtation on the Antiquity of the Earth. Read at the Royal Society, 12th May, 1785. By the Rev. James Douglas, F. A. S. 4to. 10s. 6d. in Boards. Nicol.

A Differtation on the Antiquity of the Earth, read at the Royal Society, printed in a handfome quarto, adorned with engravings in aqua tinta, promised great information. We read the preface without understanding it; but this might have been written in hafte; it might have been the work of a friend, no uncommon device: the Differtation itself would repay us for the loft time: at least we were fure of the plates. But let our readers learn from our misfortunes: Bleffed are they who expect nothing, for they fhall not be disappointed.' Almost all our expectations were frustrated. The work itself we can give very little account of, for this very obvious reafon, that we understand very little of it: we should be glad

to

to know if the author himself has any decided opinion on the fubject. The plates are in fome inftances ufelefs, and in others fo little like the appearances of which they are faid to be copies, that, what the author ftyles the head of a pike, we really thought was intended to reprefent a sheep's heart. Some of the antiquities, and fome of the foffils, are very accurately reprefented in this way; and the engravings of medals are fuch faithful copies, as to fully justify our recommendation of this method of imitating them. We gave this opinion in reviewing Mr. Coombe's account of Dr. Hunter's medals; but it has not been publicly practifed, except in the work before us: we hope it will now become more common.

It may be neceffary to produce fome proofs of our affertions. We fhall felect, therefore, the first part of the preface.

Metaphyfical truths can only be established, by producing effects from correfponding caufes; and though we may confront fuch demonftrative evidence with the immutable laws of mathematical decifion, we must be fenfible that there will still remain fome pretence for doubt; thus the bafis of that knowledge, which on these principles we have been long labouring to accomplish, will become an endlefs toil, an endless fource for controverfy and having the paffions and the prejudices of mankind to combat, which mathematical certainty can alone effectually fupprefs, we must content ourfelves only with making converts of those who have minds fufficiently expanfive to listen to hypothetical arguments, without the fhackles of Euclid, and the vanity of difplaying their own learning and pedantry.'

We shall make no obfervations on this paffage, for we would engage rather to explain the most enthusiastic reveries of the wildelt alchemist.

A foffil was difcovered at Chatham, in a bed of river-fand, mixed with a kind of clay, about twenty feet above the level of the river Medway, at high-water mark. It appears to be part of a jaw-bone, and it is extremely curious, both from its fize, and the number of its molares. It is now in the Museum, which was fo lately the property of fir Afhton Lever. The other bones were found alfo, but they are not preserved. On comparing this jaw-bone with one of an hippopotamus in the fame collection, the fimilarity was fo ftriking as to convince the author that both belonged to an animal of the fame fpecies. Mr. Douglas, eager to purfue all the confequences of this fuppofed difcovery, immediately concludes, that this part of the earth was once warmer than it is at prefent; that thefe bones were not brought here by the deluge, but muit have been the exuviæ of an animal actually exifting on the fpot. All the reft confifts of cafes and data. The cafes contain facis chiefly intended to fhow, that the animal gluten is