employed to transfer to prints the tints of an original drawing.

The minerals reprefented in this work are mostly extracted from the mines of Cornwall, and not a few of them are peculiar to that district. The fibrous tin ore, very improperly called wood tin, has never been found elfewhere; and the continental mines have only produced very imperfect fpecimens of arfeniate of copper, a fubftance whofe beautiful and numerous varieties have been the fubject of the accurate analyûs of Mr Chenevix, and of a cryftallographical defcription by the Count de Bournon, in the Philofophical Tranfactions. Mr Rafhleigh has favoured us with a drawing of hydrophanous chalcedony invefting tin ore. We are furprised that the beautiful ftalactitic capillary and invefting chalcedonies of Trevafkus mine have been omitted by him, and that he has given us no drawing of the fchorls, of which Cornwall produces beautiful fpecimens. The phosphates of lime adhering to talc, prefent fome of the rare cryftalline modifications; but no notice is taken of them, or of the capillary native filver of Herland mine, or of many other fingular products of the country. Such minerals would, we think, have proved more generally interefting than the Derbyshire calcareous fpars and fluors, or the fofil fhell and the echinus in fluid, which laft is far from appearing to us a clear demonftration of the Neptunian origin of the flint. The agency of the aqueous formation would have been more ftrikingly illuftrated by fome of the fpecimens of martial pyrites invefting pieces of unaltered wood, and fometimes completely affuming its form, by pervading its fubftance; which are abundantly found in the peat that cos the gravel mixed with tin ore at the fteam work at Carnon.

ART. IX. A Syftem of Chemistry. In Four Volumes. By Thomas Thomfon M. D. Lecturer on Chemiftry in Edinburgh The Second Edition. Edinburgh: Printed for Bell & Bradfute and E, Balfour; G. & J. Robiufon, London; and Gilbert & Hodges, Dub lin. 4 vol. 8vo. 2638 pages.

THE

HE first edition of this work was published a little while before the commencement of our undertaking; and we are much pleafed to find that its fuccefs has been fo great, as already to give us an opportunity of noticing it in its prefent improved ftate. With the very great merits of the former edition we were well acquainted; and muft regret, with every lover of the fcience, that it met even with one folitary inftance of uncandid feverity.

We

We perused the firft part of the preface with much fatisfaction. We admired the author's fpirited defence of the state of chemistry in Britain, against the mifreprefentations of foreigners; and fully fubfcribed to the juft encomium which he finds it neceffary to pronounce on his own merits. The fecond part, however, in which he in fome measure developes the plan of his work, rather checked our growing partiality; for, inftead of returning thanks to our fellow labourers on the other fide of the Tweed, for the almoft unqualified approbation which they beftowed on his former edition, or foliciting the fame attention to the prefent, he boldly fets our whole corporation at defiance, and denies the competency of our tribunal. Indeed, it is not difficult to difcover that it is the Doctor's honeft opinion, that no perfon is qualified to judge of his performance but himself; for who elfe is there who has the fame turn of thinking, who poffeffes the fame information, and who has bestowed on the subject the fame patient meditation?' In the defeription of thofe capable of criticizing his arrangement, he is, if poflible, ftill more faftidious. They must not only poffefs all the neceffary mental qualifications, but they must be authors or teachers, and must have no arrangement of their own. In short, Dr Thomfon's arrangement must not be criticized. But if, in our author's opinion, extraordinary qualifications be neceffary to judge of his plan and arrangement, ftill more extraordinary abilities were neceflary to contrive it. Few confider that the art of arranging is one of the most difficult talks of the philofopher; that it requires a comprehensiveness of mind, a clearnefs of judgement, and a patience of labour, which fall to the lot of a fmall number only of the human race. Whatever Dr Thomfon may think of his own abilities, compared with thofe of other men, there is certainly fome degree of imprudence in this publication of his fentiments; for he ought to be aware, that though men may fometimes forget to applaud the modesty of an author, they never fail to refent his arrogance.

The object of this work is to exhibit as complete a view as poffible of the prefent ftate of chemistry, and to trace at the fame time its gradual progrefs, from its first dawnings as a science, to the improved ftate which it has now attained.' It alfo comprehends the application of that fcience to fubftances as they exift in nature, conftituting the animal, vegetable, and mineral kingdoms.' The plan, abftractly confidered, is excellent; but there have been, it feems, fome people fo narrowminded, and others fo extravagant in their ideas, as not to be pleafed with it; the one fet pretending that it contains too little, the other that it contains too much. Thefe oppofite opinions,

our

our author thinks, refute and exactly neutralife each other, and fuggeft to him this very comfortable conclufion, that in all probability he has not deviated very far from that happy middle path which he ought to follow. But, in the fulness of his joy, he feems to have forgotten that these premifes afford room for another conclufion, namely, that it may contain too much of what it fhould not contain, and too little of what it should contain; too little chemistry, for example, and too much extraneous matter. This, at least fo far as regards the manner in which the plan is executed, appears to us to be really the cafe; but our reafons for entertaining this opinion, will appear as we proceed in the analysis of the work.

The work is divided into two principal parts; the first comprehending the fcience of chemistry, and the fecond the chemical examination of nature. The first part contains three books, which treat, in fucceffion, of fimple fubftances-of compound bodies-and of affinity. The two firft claffes are again divided and fubdivided into orders and fpecies. Nothing can be more fimple, fcientific and beautiful than the arrangement. Indeed, our author feems fo much enamoured of it himself, that he gives it as his decided opinion, that if this work poffefs any fuperiority over others, if it be more perfpicuous or complete, we muft afcribe it to the arrangement. The fuperiority of this book to most other systems of chemistry we are not difpofed to deny; but we are lefs inclined to afcribe it to the merit of the arrangement, than to the circumftance of its having been written after all the other fyftems, and to the patient industry of the author in obferving and collecting facts. Indeed, fo well has Dr Thomfon availed himfelf of thefe advantages, that we have no doubt but his fyftem will be confidered as a valuable repofitory of facts long after the peculiarities of its arrangement thall be forgotten. It may appear ftrange, that we fhould value at fo low a rate an arrangement which, we are told by its contriver, is independent of hypothefis, and as nearly inductive or analytical as was confiftent with the state of the science, which prefuppofes no previous knowledge of the fubject, and begins with thofe parts which have been moft fuccefsfully inveftigated, and which therefore admit of a plainer and fimpler mode of illuftration.' To the whole of this eulogium, however, we can by no means fubfcribe; on the contrary, we are inclined to think that an arrangement, poflefling all the advantages he defcribes, is, in the prefent ftate of the fcience, impracticable; and that Dr Thomfon himself has found it fo.

The first peculiarity of Dr Thomfon's arrangement, is the attempt to communicate the knowledge of a phyfical fcience in the fame way in which it was originally acquired, by fimply ftating, in

the

the first place, all the particular facts, and gradually afcertaining the general laws by induction. This method certainly poffeffes one. evident advantage. The general principles of the fcience can be afterwards explained in the fulleft and most fatisfactory manner, as we are already in poffeffion of the immenfe mafs of facts from which they are derived, and by which they may be illuftrated. But the difadvantages with which it is attended are infinitely greater. From having no general principles to direct us. at the outfet, the detail of facts must be dry and uninteresting; their relative importance cannot be perceived when they are ftated; their connexion with each other will be overlooked, and they will be remembered with infinitely greater difficulty; while the general doctrines may be fufficiently explained by numberlefs familiar facts and illuftrations, easily understood by every one entering on the ftudy of chemistry. Thus, Dr Thomfan himfelf, under the very firft article, Oxygen, finds himself obliged to explain the general doctrine of Allinity; and under, the fecond, Sulphur, gives an account of the different theoriesof combuftion. We are therefore inclined ftill to prefer the. common didactic method of firft explaining the more general doctrines, to Dr Thomfon's apparently more philofophical arrangement of arriving at all his general doctrines by induction.

The other peculiarity of Dr Thomfon's arrangement, if we can call that a peculiarity which has been adopted by others, is. the divifion, of bodies into fimple and compound. Now, the Doctor has told us, that very poffibly the bodies, which we reckon fimple, may be compound; but, till this has been actu-" ally proved, we have no right to fuppofe it;' and as some subftances which have not been decompofed, are very analogous in their properties to others whofe compofition is afcertained, it neceffarily follows, that if we arrange them among the compound bodies, our fyftem becomes hypothetical; and if we rank them as fimples, it becomes artificial and unnatural. Befides, there are very few, even of thofe which are confidered as fimple: fubftances, which ever were the objects of any of our fenfes, except in a state of compofition. Let us examine, for instance, thofe called fimple fubftances by our author. His unconfinable bodies, light and caloric, are refrangible, and may be decompofed into rays. Of the confinable fubftances, the metals and fimple combuftibles, according to the hypothefis which our author adopts, are compounds of an unknown bafe and light. Azote and muriatic acid are fufpected by him to be compounds. At any rate, they, as well as oxygen (the only remaining fimple fubftance) never exift but in a ftate of combination.

But even granting, for the fake of argument, that the prefence

of

of the unconfinable bodies does not make fubftances compound, which would otherwise be fimple, Dr Thomson has found himself under the neceffity of departing moft materially from the principles of his arrangement, the moment he attempts to apply them. Two alkalies and nine earths, although they have never been decompofed, are claffed by him among the compounds; and, on the contrary, of thirty-feven acids, three only have not been decompofed; and of thefe three, two are left among the compound bodies; while one, the muriatic, is feparated from all the others, and placed among the fimple fubftances. Nothing can demonstrate more forcibly that these principles are either fundamentally erroneous, or at least inapplicable in the prefent ftate of the fcience. The earths and alkalies are claffed with compounds, not only on account of their analogy to ammonia, but because all other fimple bodies, it feems, are connected together, either by common properties, or by the part which they act in combustion; whereas these have no fuch connexion. The latter of these two arguments is of no weight whatever; for it certainly does not follow, that becaufe fome fimple bodies have an affinity for oxygen, all fimple bodies must have fuch an affinity. The analogy to ammonia is not more fatisfactory; for if Dr Thomfon had followed up his own principles of arrangement, and divided compounds, as he has done fimple bodies, into fupporters, combustibles, and incombuftibles, the fubftances in queftion must have been feparated from ammonia; that alkali being combuftible, and the earths and other alkalies incombuftible. The analogical reafons for claffing the muriatic acid among fimple bodies, are still lefs convincing. Even muriatic acid,' fays our author himfelf, though its refemblance to azote is ftriking, differs from it in fo many particulars, that I dare not venture to feparate it from the clafs of acids under which it has been hitherto arranged.' Since our author himself confeffes that azote, and muriatic acid, differ in many particulars from each other, it will fave us the trouble of proving it; but we must observe, that although he has not ventured to feparate muriatic acid from the clafs of acids, an account of its characteristic properties occupies the second section of the chapter on fimple incombuftibles, while, in compliance with the ufual cuftom of chemifts, he has referved an account of the properties of liquid muriatic acid for the chapter on acids, where it is again mifplaced among the acid fupporters. In all this, there is much of that inconfiftency which muft neceffarily arife when we attempt to accommodate facts to an arbitrary and artificial fyftem.

His fimple fubftances are subdivided into confinable and unconfinable. One reafon given for employing thefe words, is fa

tisfactory