the late Dr. Shaw, and Mr. Hawkfbee (to whom the prefent tafte for. chemical experiments, is in a great degree owing), that in the year 1731 they published, with confiderable additions to Becher's tract, a finall volume entitled, "An Effay for introducing a Portable Laboratory", for which, as they ing nuoufly acknowledge, they were almott whol ly indebted to Becher. The furnace defcribed by Dr. Shaw and Mr. Hawkfbee differs little from that of Becher, and, like it, is in tended to be lined with a lute, which is to be fecured to the iron plate by means of rivets. "This has been hitherto almoft the univerfal practice in forming portable furnaces for chemical ex periments; and it is but juftice to fay, that to these authors are to be afcribed the invention and introduction of furnaces on this conftruction, however the fh pes may have been varied fince their time. "Another kind of portable furnaces, if they may be faid to de ferve the title, were contrived by Johanne Francifco Vigani, and the defeription of them, with figures, published by him in a fmall treatife entitled, Medulla Chymiæ; printed in London 1683, and dedicated to three English noblemen. "As thefe furnaces confifted folely in having a number of bricks, fo fitted together and marked, that they might eafily be taken afunder, when an operation was finished, and commodioutly fet afide until they fhould be again wanted, the frequent miflaying, or lofs of the loofe bricks, foon brought this kind of furnace into difufe, in experimental laboratories; though it must be owned, it has in many cafes fome advan ages, and is often ufed, to this day, by plumbers, and other workmen. "About the year 1750, the late Dr. Lewis, whofe name and memory will ever be refpected by all votaries to chemistry, obferving the inconveniencies that attended the ufe of both the foregoing kinds of furnaces, and taking the hint, as he candidly acknowledges, from an ingenious workman, and alfo reflecting on the durability of black lead crucibles, and the ease with which the openings for doors, chimneys, &c. are made in them, contrived thole portable furnaces, fo accurately, and fo properly defcribed by him, in the first part of his excellent work, entitled, The Philofophical Commerce of Arts; a work, which if he had met with due encouragement to profecute, and had completed according to his ideas on the fubject, would have done infinite honour to himself and to his country. Since that time, it does not appear that any one has made an effential alteration in the construction of these kinds of in ftruments, except the ingenious Meffrs Ruhl and Hempel, of Cheyne Row, Chelfea, who having, under the patronage of the Society, eftablished a manufactory of black lead pots, and profiting by the thoughts of Dr. Lewis, have employed themselves in making fur naces, in a very neat and commo. dious manner, of the fame materials their pots are formed of; and the only objection to them, is the price at which they must neceffarily be fold, on account of the value of the materials, and the workmanfhip; in every other refpect, they anfwer well the purposes they are intended for, being ingeniously contrived, and executed in a workmanlike manner, "It would be highly improper here to omit obferving that the justly admired Boerhaave, mentions two two kinds of portable furnaces contrived by himself, the one formed of wood, lined with iron plate, in which only thofe operations that require a very gentle hear, hardly exceeding that of boiling water, could be performed. As in this furnace, a fmall equable fire may conveniently be kept up without much trouble or expence, he calls it, Furnus Studioforum. His other furnace he directs, like thofe of Becher, to be made of plateiron, but lined with brick fet in mortar made of lime and fand; this furnace, however, as defcribed by him, feems too large for experiments, and in ftrong heats, every one knows how improper it is to have lime come in contact with the bricks, which are liable to be greatly injured by it, and indeed, neither of thefe furnaces have thefe many years past been much used. The celebrated Pott, in his treatife, entitled Lithogeognofia, alfo defcribes a portable furnace, of which a defign is annexed to his work; in this furnace, he fays every thing in nature, that is fufible, may be melted in an hour or two. He acknowledges this furnace to be very fimilar to that of Becher, and defcribes the lute he lined it with, as compofed of equal parts of pipe-clay, burnt and unburnt, mixed together and moiftened to the confiftence of pafle, with bullock's blood: it is evident this will be fubject to all the inconveniencies of the other furnaces lined with lute. "The principal objection that has arifen against the furnaces of Becher and Shaw, is that the lute, being a mixture of fand, clay, and water, muft neceffarily fhrink, and confequently crack in drying; but this evil may in fome degree be remedied by filling up the cracks, when dry, but before a fire is lighted, with fresh lute, which will, if artfully managed, adhere pretty well to the firit layer: but there ftill remains an infuperable obftacle, which is, the iron rivets that pafs through the fides of the furnace, into lute, expanding in great heats, and contracting with cold, in a degree very different from that of the mixture of clay and fand that furrounds them, they are continually cracking the lute, and ferve rather to feparate and throw it off from the iron plate, than to retain and fix it. The chief objection to the black lead furnaces of Dr. Lewis, is the thinnefs of the crucibles of which they are formed; this not only permits a large proportion of heat to escape, but when the furnace grows red-hot, tends very much to incommode the operator, and heat the room wherein any experiments are making. "It is with a view to remedy thefe inconveniencies, rather than to propofe any new form of a furnace, that this paper is fubmitted to the confideration of the fociety; and this end is obtained by uniting, in fome degree, the three above mentioned contrivances, by adopting the iron of the furnace of Becher, the bricks of Vigani, and the fize of Dr. Lewis, which seems beft adapted to experimental enquiries. "To form the body of the furnace, which is the only part intended to be here defcribed, (as any perfon converfant with thefe machines, will readily fafhion the dome and other parts as may best. fuit their intention;) procure a cylinder, about eleven inches in diameter, and twelve or fourteen in length, made of strong plate iron, rivetted together; or, as the thick nefs : nefs of the lining, will prevent its ever becoming hot enough to melt hard folder, it will be much neater, if the joint be brazed at one end, which is to be confidered as the bottom of the cylinder, a piece must be cut out about four inches fquare, which is to be the opening to the afh-hole, to this an iron door is to be fitted; just above this opening, three iron pins, project ing half an inch or more withinfide the cylinder, must be well rivitted on, at equal distances from each other; four or five inches above these pins let another hole be cut in the iron cylinder, and a door fitted to it, this ferves for putting in the fuel, when the furnace is ufed for diftilling, and fuch operations as require only a gentle heat. "On the pins before mentioned, lay an iron grate, and let the whole of the cylinder, above this grate, be lined with fire-bricks, the joints well fitted, and laid in loam; by this means the objection to the lute of Becher and Shaw, is obviated; and as the bricks may be left an inch and half or more in thickness, the heat will be better retained than in the black lead furnaces of Dr. Lewis. To fecure the iron door, whenever the furnace is to be used as a wind hole, or any ftrong fire raised therein, a piece of fire-brick is to be fitted to the opening, and the door fhut, which will effectually preferve the iron from injury. It has been cuftomary to make portable furnaces in the form of a truncated cone, the finaller end being the lower part, that different fized grates, may fit at different heights; if this fhape is till thought eligible, it may be eafily obtained, by leaving those bricks that are next the grate, thicker than those towards the upper part, and the diminution may either be regular, or projections left at the heights required, on which the different grates may rest. "Fire-bricks, fit for this purpofe, are easily obtained in every part of this kingdom, and in London they are conftantly to be met with, at a low price, being fent hither of two kinds, under the names of Windfor bricks, and Nonfuch bricks; the first fo called from being brought from the town of that name, and the other from their being made at Nonfuch Park, near Epfom, Surry: thefe bricks stand every degree of fire well, and are of fo soft a texture, as readily to admit of cutting and grinding into any form required, fo as to be cafily adapted to the figure of the furnace; and as the loam or earth of which they are made, is alfo brought to town for fetting them, that alfo may be readily obtained; and thus fmall portable furnaces, more durable, and better adapted to the making chemical experiments than any have hitherto met with, are e fily and at little expence constructed. "The very refpectable authors I have already quoted, have given fuch precife and accurate defcriptions of the forms beft adapted to the ufes intended, that no additions need be made to their works on that head; and the well known furnace of Dr. Black of Edinburgh, when lined with bricks, as now recommended, will be found greatly to exceed in utility, thofe which having been hitherto lined with lue, have been liable to the objections ftated above." NATURAL NATURAL HISTORY of the GIANT's CAUSEWAY. [From LETTERS concerning the Northern Coaft of the County of ANTRIM, &c. By the Rev. WILLIAM HAMILTON.] "T HE vicinity of the little tifling village of Portrush to the Giant's Caufeway, has afforded me, during my itay here, ample opportunity to vifit that curious work of nature, and to examine, with a good deal of attention, the features of the adjoining country, which has hitherto been very imperfectly known. "The Causeway itfelf is generally defcribed as a mole or quay, projecting from the bafe of a teep promontory, fome hundred feet into the fea, and is formed of perpendicular pillars of bafaltes, which ftand in contact with each other, exhibiting an appearance not much unlike a folid honeycomb. The pillars are irregular prifms, of various denominations, from four to eight fides; but the hexagonal columns are as numerous as all the others together. On a minute infpection, each pillar is found to be feparable into feveral joints, whofe articulation is neat and compact beyond expreffion; the convex termination of one joint always meeting a concave focket in the next; befides which, the angles of one frequently fhoot over thofe of the other, fo that they are completely locked together, and can rarely be feparated without a fracture of fome of their parts. "The fides of each column are unequal among themfelves, but the contiguous fides of adjoining columns are always of equal dimenfions, fo as to touch in all their parts. "Though the angles be of va rious magnitudes, yet the fum of the contiguous angles, of adjoining pilars, always makes up four right ones. Hence there are no void fpaces among the bafaltes, the furface of the causeway exhibiting to view a regular and compact pave. ment of polygon ftones. "The outfide covering is foft, and of a brown colour, being the earthy parts of the ftone nearly deprived of its metallic principle by the action of the air, and of the marine acid which it receives from the fea. "Thefe are the obvious external characters of this extraordinary pile of bafaltes, obferved and defcribed with wonder by every one who has feen it. But it is not here that our admiration fhould ceafe; whatever the process was by which nature produced that beautful and curious arrangement of pillars fo confpicuous about the Giant's Caufeway; the, caufe, far from being limitted to that fpor alone, appears to have extended through a large tract of country, in every direction, infomuch that many of the common quarries, for feveral miles around, feem to be only abortive attempts towards the production of a Giant's Caufeway. From want of attention to this circumftance, a vast deal of time and labour has been idly fpent in minute examinations of the Caufe way itself; in tracing its courfe under the ocean, purfuing its columns into the ground-determining its length and breadth, and the number of its pillars-with nume rous wild conjectures concerning its original; all of which ceafe to be be of any importance, when this fpot is confidered only as a fmall corner of an immenfe bafalt quarry, extending widely over all the neighbouring land. The leading features of this whole coaft are the two great promontories of Bengore and Fairhead, which stand at the distance of eight miles from each other: both formed on a great and extenfive fcale, both abrupt toward the fea, and abundantly expofed to obfervation, and each in its kind exhibiting noble arrangements of the different fpecies of columnar bafaltes. "The former of thefe lies about feven miles west of Ballycastle, and is generally described by feamen, who fee it at a distance and in profile, as an extenfive headland, running out from the coaft a confiderable length into the fea; but, ftrictly speaking, it is made up of a number of leffer capes and bays, each with its own proper name, the tout enfemble of which forms what the feamen denominate the head land of Bengore. "Thefe capes are compofed of a variety of different ranges of pillars, and a great number of trata; which, from the abruptnefs of the coaft, are extremely confpicuous, and form an unrivalled pile of natural architecture, in which all the neat regularity and elegance of art is united to the wild magnificence of nature. "The moft perfect of thefe capes is called Pleafkin, of which I fhall attempt a defcription, and along with it hope to fend a draw ing which my draftfiman has taken from the beach below at the rifque of his neck; for the approach from thefe promontories down to the fea is frightful beyond defcription, and requires not only a strong head, but very confiderable bodily acti vity to accomplish it. "The fummit of Pleaskin is covered with a thin graffy fod, under which lies the natural rock, having generally an uniform hard furface, fomewhat cracked and shivered. At the depth of ten or twelve feet from the fummit, this rock begins to affume a columnar tendency, and forms a range of maffy pillars of bafaltes, which stand perpendicular to the horifon, prefenting, in the fharp face of the promontory, the appearance of a magnificent gallery or colonade, upwards of fixty feet in height. "This colonade is fupported on a folid base of coarse, black, irregular rock, near fixty feet thick, abounding in blebs and air holes ; but though comparatively irregu lar, it may be evidently observed to affect a peculiar figure, tending in many places to run into regular forms, refembling the fhooting of falts and many other fubftances during a hafty crystallization. "Under this great bed of flone ftands a fecond range of pillars, between forty and fifty feet in height, lefs grofs, and more sharply defined than thofe of the upper ftory, many of them, on a clofe view, emulating even the neatnefs of the columns in the Giant's Caufeway. This lower range is borne on a layer of red ochre ftone, which ferves as a relief to fhew it to great advantage. "Thefe two admirable natural galleries, together with the inter jacent mafs of irregular rock, form a perpendicular height of one hundred and feventy feet; from the bafe of which, the promontory, covered over with rock and grafs, flopes down to the fea for the fpace of two hundred feet more, making |