P. 79. Platina is not a metal in the common acceptation of the word. Lehman and Buffon have lately proved that it ought never again to appear among metals.

Lehman, Marcgraff, and Adanfon, had native iron long

ago.

P. 81. Manganese and emery belong rather to the author's cryptometalline foffils, and contain very little iron, if any at all, especially emery.

P. 83. Native Lead has hitherto not been found.

P. 85. Prof. Brunnich, in the last edition of Cronsted's Mineralogy, very juftly doubts that native tin has been difcovered.

Arfenic is not properly a metal, but belongs to the faline bodies having all their properties.

P. 86. Black Jack ought to be ranked among our author's cryptometalline fofils.

P. 89. Nickell is at prefent known not to be a separate metal, but rather a inixture of several.

Molybdana, or black lead, contains fome metallic particles, but they are fo much furpaffed by fulphur, that it cannot be ranked among metals.

P. 91. Cryptometalline foffils are metallic ores, and ought not to be feparated from the metals, nor can they with any propriety form a feparate clafs of foffils.

P. 109. The author reckons bafaltes among the flares metallici, and is very much mistaken, for they are a lava or melted fubftance, produced by a fubterraneous fire. Another mistake of our author is, when he makes bafaltes, and sherl, or cockle, fynonimous, for though herls are often contained in bafaltes, in the fame manner as feldspat or mica in granite, no mineralogift, however, would venture to call her bafaltes, or feldspat granite. Vide Raffe's Account of the German Volcanos, who has treated this fubject in the most fatisfactory manner.

P. 110. Bafaltes of a pyramidal, and of a columnar figure, are certainly put here by mistake, and we dare fay, the author had fher of this conformation in view, but did not know how to diftinguish them from bafaltes. We wish, likewife to know the reafons which induced our author to speak here again of bafaltes as a metallic flos, having already ranged it, p. 57, among the genus of faxum vulgare.

P. 111. Every reader finding here the fpirit of vitriolic acid, in a fluid form, will naturally fuppofe the author knows fome fpot of our globe where, this acid is fell in fuch a fluid form; but if this be the cafe, we hope the author will be fo kind to inform the more ignorant mineralogifts where fo extraordinary a phenomenon is to be met with.

Thefe

These few remarks will convince our readers, that this publication is by no means calculated to become a useful guide in mineralogy; and though the author promifes, after a period of years, to republifh his performance more perfect, we have reafon to believe, that even then it will be of little value. The best advice for our author would be to learn chemistry of the celebrated Dr. Fordyce, or Dr. Higgins, or that great mafter in this fcience Mr. Woulfe; to travel over Great Britain and Germany, to examine all mineral fubftances in their beds, to inspect the various mines, to collect materials, to fubject them to a chemical examination, then to read what has been faid by others; and laftly, to fet about an entire new work on mineralogy; and we have not the least doubt, but it will be widely different from the prefent publication, and more acceptable to the public.

cui lecta potenter erit res, Nec facundia deferet hunc, nec lucidus ordo.

HORAT.

A Compleat Treatife on Perspective, in Theory and Practice; on the Principles of Dr. Brook Taylor. By Thomas Malton. Fol. 21, 5s. Boards. Robfon.

Perspective is one of thofe fine imitative arts which are not

only profitable but very entertaining in the execution, and is a genteel accomplishment to every perfon of a liberal education.

It is not a fallacious art, as has been imagined by fome perfons who are ignorant of its principles; but it is truly mathematical, and fubject to the strictest geometrical demonftration. It requires, indeed fome judgment to apply it with any propriety, and to produce the moft pleafing representations of objects. And to demonftrate and explain its principles, and to direct the judgment in the proper application of them, many perfons, and fome of refpectable character, have given to the world the refult of their labours in this way; as Vignola, Marolois, Defargues, de Boffe, Albertus, Friefe, Lamy, Niceron, Pazzo, the jefuit, Ditton, s'Gravelande, Taylor, Hamil ton, &c. The two laft mentioned refpectable perfons in particular feem to have perfected this fcience; Dr. Taylor by his explanation of its most easy and general principles of practice, and Mr. Hamilton by his ftupendous performance on this fubject. Many other ingenious artists have also published large comments on the principles thus happily explained, by many examples of application to purposes of real and frequent ufe, with ample directions for particular cafes; and among the reft the ingenious and industrious anthor of the work now before us. And although the principles of the art be fo few

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and

and fimple, yet when its various applications are fully made and explained, it will not be matter of wonder that it should employ a folio volume, as in the prefent inftance.

I do not pretend, fays the author, to have found out new principles, nor do I think, there can or need be any other; those given by Brook Taylor, being fufficient for any purpose, whatever; and that, the principles, on which he has founded his fyftem, are the most fimple and perfect that can poffibly be con

ceived.'

And again,

Now, although I have not the leaft pretence to the invention of new principles, yet I am firmly perfuaded that I have made use of those we have to the best advantage; that, from the irregular and imperfect order, as they are given Dr. Brook Taylor, I have digefted it into an useful and practical system; not involved in a labyrinth of mathematical demonstration, of things which are to little purpofe in the art of delineating.'

He has, however, given fuch mathematical demonstrations of the principles which he has laid down, as appear to be neceffary for real practice.

This work is divided into four books; the first treats of Optics or Vision, the fecond of the Theory of Perspective, the third of the Practice of Perspective; and the fourth of Shadows. Each book is fubdivided into fections: thus the first book contains five fections; viz. 1. A Differtation on Light and Colours; 2. A Defcription of the Eye and the Manner of Vifion. 3. Treats of Dire& Vision. The 4th contains Objections to the received Opinion of the Caufe of Vision, and to many other phyfical principles. The 5th contains a few Obfervations on the subject of Refracted Light; and several objections to various other subjects, frequently reflecting on fir Ifaac Newton and other great philofophers, with whose writings our author feems not to be sufficiently well acquainted. The whole of this first book, except two theorems in the third fection, is entirely foreign to a Treatife on Perspective, and being quite out of the line of our author's subject, it is therefore impertinent, even if the objections, &c. advanced in it concerning a variety of philofophical fubjects, were judicious in themselves; but as they appear fo much the contrary, they may hurt our author's reputation, by the appearance of a prefumption arifing from a too fuperficial knowledge of the fub`jects animadverted on; and, in our opinion, it would have been better if he had entirely omitted them.

The fecond book is divided into fix fections, containing, the whole ufefu. theory of perfpective, rectilinear, and curvi linear, which is fomewhat copious, by reafon of the examples given for illuftration, and corollaries neceffarily deducible from the theorems. The first fection is a general introduction,' con

taining

taining a defcription of lines and planes, parallel, perpendicular, and inclined, either to the horizon, or any other lines and planes; and other preparatory remarks. The fecond is also introductory, and contains a full explanation of all the various kinds of projection, ichnographic, orthographic, and ftereographic; with a circumftantial and comprehenfive definition of perspective, and other introductory matters. The third is more elementary; it contains a full, yet brief definition of all the terms made ufe of in the theory. The fourth fection contains the whole theory of right-lined perfpective, in fourteen theorems; from which are deduced feveral ufeful and practical lessons in corollaries, fcholia, &c."

The demonftration of theorems are given in a very elaborate manner, and may probably appear very tedious to many readers. The diagrams alfo are frequently perplexed or indiftinct by an affectation of rendering them univerfal.'

• The fifth fection contains fo much of the theory of curvilinear perspective, as is really ufeful in practice; or neceffary to be known, by any artist whatever. The fixth is a refutation of feveral capital errors and abfurd opinions, which many perfons entertain of perfpective; and which are there clearly and fairly stated, and fhewn to have no real existence.'

We apprehend our author means by this laft expreffion, that those opinions are ill founded. And we agree with him in his objections to fuch opinions, and in his explanations of the phenomena which fometimes give rife to them; but in our opinion the difcourfe might have been placed with more propriety elsewhere than as a section of the regular work. A few paragraphs from this fection we shall extract as a fpecimen.

From the circumitance I have mentioned, fays the author, in respect of the true reprefentation and appearance being depictured, at once, on a spherical furface, fome artists imagine, that the reprefentation on a plane ought to be fo delineated; it cannot be 'tis impoffible, in the nature of things. Suppofe a true reprefentation of a long building, in full front, delineated on a spherical furface, and it were poffible, afterwards, to reduce the spherical furface to a plane; is any person so weak as to fuppofe that fuch a reprefentation would appear like the origi nal, in any point of view? he must be weak, indeed, and have strange mistaken notions of perspective, who can and yet I have heard this point ftrenuously fupported, or rather argued for (fupported it could not be), for any thinking perfon (who can think with any propriety about it) must be fenfible, that, what should reprefent right lines will be curved, and, the whole, will give the idea of a rotunda, or externally round building; feeing that, the extremes would fall off, not in right lines but curved, and they would appear lefs than the real object; to fay nothing the almoft impoffibilty of producing or delineating fnch

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fuch a picture, at all, or by any means; I fhould be glad to be informed, how, or by what rules.

I have juft bethought me of one circumftance, which, I think muft convince an atheift in perspective. I am perfuaded, no perfon will deny, that, if the eye could be fixed in a point, at a proper diftance from a tranfparent plane, placed between the eye and an object, whilst the hand traced, accurately, every line of the object, as it appeared on the transparent plane; fuch a delineation, all muft allow, would be a true one. Let thofe, who are not otherwife to be convinced, try the experiment. I will take all my knowledge in perfpective, that every reprefentation of a right line is a right line, on the plane; that columns or cylinders of equal magnitude, and parellel to the plane, will be larger as they are more remote from that point, on the plane, to which the eye is oppofite; that the reprefentation of a circle or fphere, feen oblique, is an ellipfis; that objects of equal magnitude, and equally diftant from the picture parellel to them, however otherwife fituated or elevated, will be reprefented equal; with various other circumftances; all which may be fully proved to ocular conviction, which will not admit of the leatt doubt. Surely then, if perspective performs the very fame thing, which it certainly will, in every refpect, it must exhibit a true reprefentation of objects.

It is the bufinefs of peripective to produce the figure of a fe&ion of the cone or pyramid of rays, from the eye to the object, by a plane, in any determined pofition; which, if the rules it prefcribes be truly followed, it will moft certainly effect, without any fenfible error. For, wherever any point, or angle of an object, appear on a plane, or other furface, between the eye of the object, there the visual ray would cut and pass through the plane, to the eye; but when the diftance of the eye is fuch, that the vifual rays, from the eye to the object, cut the plane very oblique, or in angles, nearly, or perhaps less than, half right ones, the reprefentation will confequently be distorted and prepofterous, and, in other points of view, will have a disagreeable and unnatural appearance.

• Flere, then, lies the miftake, which, through ignorance or inadvertency, is attributed to perfpective, and fuppofed to be a deficiency or imperfection in it. Tis, generally in the point of view, the fituation, &c. of the picture or object; which, by being too near the eye, occafions that diftortion and prepofterous reprefentation we perceive in feveral pictures; for, if the optic angle, under which the whole picture is feen, exceeds 50, or, at the moft, 60 degrees, the distance is not fufficient; as, the vifual rays will cut the picture very oblique, near its extremes, and occafion a difagreeable diftortion of the objects on the extreme parts of it. Yet, as I have observed, at any diftance, the reprefentations of columns, or other cylindrical objects, on a picture parellel to them, will, in true perspective, ever be the feaft which are nearest to the center.

! I fhall