that in which they have been ufually confidered. In the feveral problematical points which fall under his examination, though he may not perhaps always maintain the most defenfible fide of the argument, yet where he does not convince, he feldom fails to intereft and amufe, by his ingenuity and the vivacity of his manner, and of his ftyle; which is, in general, lively, pointed, and farcaftical, and very much refembles that of Voltaire; while he fuccefsfully emulates the eloquent, defcriptive pencil of Buffon, in other parts of this work; which contains the refult of a very extenfive reading, and of much reflection.

ART. VI,

L'Art des Experiences, &c.-The Art of performing Philofophical Experiments; or Inftructions to the Experimental Philofopher, on the Choice, Conftruction, and Ufe of Philofophical Inftruments; and on the Preparation and Management of the different Drugs, or other Subftances ufually employed in Philofophical Experiments: By the Abbé Nollet, 3 Volumes 12mo. Paris. Durand. 1770.

HE experimental philofopher who is unfortunately fituated

THE at a diftance from the numerous artifts, whom he has

occafion to employ in the conftruction of his various machines or inftruments; or who being already poffeffed of a tolerable apparatus, is defirous of being able to rectify or improve it, and adapt it to the purposes of new and particular experiments: in fhort, who would wish to be in a capacity of realifing with his own hands, and without lofs of time, the ideas which país in his head; and would free himself as much as poffible from the inconveniences arifing from the mifconceptions, inaccuracies, and delays of mere workmen, will meet, in this very valuable work, which may be confidered as the author's lat Jegacy to the philofophical world *, with a great deal of useful and very particular information. He will here be inftructed in what manner all the members of the various inftruments and machines, defigned for the proof or illuftration of philofophical principles, are conftructed; in the nature and choice of the different materials beft adapted to the defign; and in the manner of working and forming them, fo as to answer the par ticular purposes for which they are intended.

The prefent work may be confidered as a fequel to the author's Legens de Phyfique, or lecturcs on experimental philofophy; the fixth or laft volume of which was published, in the fame form as the prefent, in the year 1764. When the Abbé pub

The Abbé, as we have been informed by the public prints, died a few months ago, in a very advanced age, at Paris.

lifhed the first volume of that work, he expreffed his opinion, that he fhould do an acceptable fervice to his readers and to philofophy in general, by defcribing, in a circumftantial manner, the various methods by which every machine or inftrument there delineated was conftructed; and by explaining the means by which it produced the effects expected from it; but confidering that fuch particular defcriptions would too much interrupt the thread of his difcourfe, he then formed the defign, and in the first and fome of the fubfequent volumes promifed to undertake the execution, of the prefent work, for the ufe of thofe who might choofe to repeat the experiments there related, or those of S'Gravefande, Defaguliers, and other writers, by means of machines, either of their own conftruction, or formed under their own direction.

In the execution of this plan, the Author, in the first volume of this work, brings the reader acquainted with all thofe preliminary branches of knowledge which are neceffary or proper to be known by the experimental philofopher, who would be his own artificer; or who would, at leaft, with to be acquainted with the mechanical or other means employed in the performing of philofophical experiments. Accordingly in the three chapters into which the first part of this work is divided, the Abbé treats of the three principal matters which are chiefly ufed in the conftruction of philofophical inftruments; wood, metals, and glafs. He begins with the art of working in wood; treats of the choice of the various kinds, as adapted to the different parts of machines; and deferibes the different tools and manauvres of the joiner and the turner. His directions to his philofophical apprentice are explained by figures of the inftruments themselves, engraved on copper-plates; of which the whole work contains fifty-fix, and which, though executed on a fmall fcale, are not crowded or confufed; as they are drawn with great precifion and neatness. In the fecond chapter, the Abbé gives fome fhort directions relative to the qualities and choice of different metals, employed in the conftruction of various inftruments; and treats of the melting, forging, hardening, turning, foldering, polishing, and other operations performed upon them.

Glafs, on account of its tranfparency, and other qualities, forms a very capital article in a philofophical apparatus. The Abbé accordingly in his third chapter treats of all thofe operations, which it may be in the power of his philofophical difciple to perform upon it, after it comes out of the hands of the glaffman; fuch as cutting, perforating, grinding, and polishing it. But of all the operations executed upon glafs, there is none which it is fo convenient for the experimental philofopher to become acquainted with, as that of melting and drawing or

blowing

blowing it into different forms, by means of the flame of a lamp, directed upon it by the blow pipe. The Author describes an apparatus for this purpose, refembling that employed by the enamellers, and by thofe who prepare glaffes for thermometers, hydrometers, and other fmall philofophical inftruments. He afterwards defcribes a more fimple method of performing the fame operations, in which a strong and continued blast is produced by means of the vapour iffuing from a boiling fluid. As the inftrument which the Abbé ufes for this purpose, and of whose effects we have, fince the perufal of this work, had fome little experience, is infinitely preferable on many accounts to the common blow-pipe, is lefs complicated and expensive than the preceding apparatus, and may eafily be constructed by any tinman, we shall probably gratify fome of our philofophical readers by giving a fhort defcription of it.

A thin and hollow tin globe is to be procured of about three inches and a half in diameter. The Author has omitted to mention the best dimenfions; but fuch is the fize of one of these inftruments now before us, which compleatly answers the intention. A hollow pipe of the fame metal, about five or fix inches in length, and bent to an obtufe angle at about two inches from the ball, is to be foldered to it, and is to be formed gradually tapering, like the blow-pipe, towards the farther extremity; where its aperture must be fo fmall as to admit only the point of a fine needle. One third of the capacity of this little Eolipile being first filled with common fpirits, or equal parts of rectified fpirit of wine and water, it is to be placed on a ftand over a lamp, fuch as that which is used for the tea-kettle. A common oil lamp is to be provided, the wick of which is to be brought near the extremity of the tube; from whence, as foon as or before the liquor in the Eolipile acquires a boiling heat, a ftrong and regular blaft will proceed, by means of which the heat of the flame will be fo greatly increafed, that even pretty large tubes will be foftened and even melt in it, and the operator may commodiously perform nearly all thofe operations on glass, which may be executed with the other more complex apparatus mentioned above.

Towards the conclufion of this chapter, the Abbé gives a particular description and delineation of a little furnace and moulds, invented and used with fuccefs by the late M. Paris, optician at Paris, for making prifms, large concave and convex mirrors, and other philofophical inftruments of glass, which are of a confiderable thicknefs. Moulds are prepared of the figure required, into which a piece of the choiceft looking-glafs is to be put, and fubjected just to such a degree of heat, as will not abfolutely melt it; as the metal might in that cafe contract fome tinge, or impurities from the mould; but merely fufficient

te

to foften it, fo as to make it fink gently into, and take the figure of the mould; out of which it is, in fome cafes, often taken, without having loft any part of its original polish. We are not fufficiently verfed in the practical part of the optician's art, to know how far this method is new; in the profecution of which, we are told the author met with difficulties: but nevertheless perfevered in his project, till he fucceeded; though diffuaded from the attempt by the Abbé, when he first propofed to him his ideas concerning it.

The information conveyed in this part of the work cannot, we think, but be acceptable and highly useful to those perfons who have a tafte and capacity for philofophical inquiries; but who are often totally unacquainted with the many eafy and fimple methods and contrivances ufed by various workmen, in the forming and adapting the different materials of which philofophical machines confift, to the purposes for which they are intended. Philofophical inquiries may certainly, cæteris paribus, be profecuted to the greatest advantage by one, who is acquainted with the principles, and can occafionally turn his hands to the practice, of thofe mechanical arts on which the conftruction of philofophical inftruments depends. It will be highly convenient to the experimentalist, to understand the language, at leaft, of the workshop, and the common proceedings of the different artificers; fo as to be qualified properly to direct them, and to avail himself, in the best manner, of their refpective talents. As to thofe who, through taste, or from œconomy, would choofe to follow the Abbé's inftructions in every point, and to execute every member, even the carpentry, of their machines, with their own hands; this part of the work will furnith them indeed with the elements of the different arts they wish to exercife: but there are numberless contrivances and manœuvres in every mechanic art, which are not to be learned in books, and which are only to be acquired by frequent visits to the workshop; to which, however, this and fome of the following parts of this work will be a very useful vade mecum.

In the fecond part, the author gives an enumeration and fhort description of fuch fimple drugs, or fuch fubftances as are generally to be had at the druggifts, as are most usually employed in philofophical experiments, and which are here arranged in an alphabetical order. He recites fome of their moft diftinguishing properties; the most obvious marks by which their general goodness may be afcertained, as well as their fitnefs for the particular ufe for which they are intended. For the information of those who may choofe to amuse themselves in the laboratory, or who may be fo fituated as not to be able conveniently to procure any particular preparations which they

may

may want from thence, this catalogue is followed by an account of the manner of performing various chemical operations. At 'the end of this first volume, the Abbé attends even to the embellishment of his machines; teaching the preparation and use of various kinds of varnishes, to be employed either on the metal or wood of which they are conftructed'; and which, at the fame time that they improve their appearance, fecure the former from ruft, and the latter from the worm, and other caufes of decay.

The contents of this volume, as the reader will perceive, are of a general nature, and have no reference to any particular fet of experiments: but in the two remaining volumes, the Author regularly proceeds through the courfe of experiments given in his lectures on experimental philofophy; explaining in the clearest manner the most minute circumstances relative to the conftruction of the machines and inftruments there mentioned, and giving particular directions to infure the fuccefs of every experiment related in that work, which requires explanation. To render thefe two volumes therefore more perfectly useful, it will be proper that the reader fhould have before him the Abbé's former work: nevertheless, as the text is every where illuftrated by plates, a reader converfant in philofophical experiments, though not poffeffed of the Abbé's lectures, will not often be at a lofs to understand the ufe and defign of the various machines, whofe parts are here feparately defcribed and delineated, and the nature and drift of most of the experiments explained in this work; which we again recommend to the philofophical reader, as a very ufeful performance: not only as a great part of the very particular and fatisfactory information which he will find in it, relative to the conftruction of philofophical machines, will, we apprehend, be abfolutely new to the generality of experimental inquirers; but as the intire performance is the production, not of a mere compiler or bookmaker, fervilely copying from preceding copyifts, but the work of an ingenious practical philofopher, who has during the greatest part of, a long life been employed, by profeffion, in explaining the principles of natural philofophy, by machines and inftruments which appear to have been principally conftructed by himfeif, or under his immediate direction: and who, in thefe volumes, has given to the public the refult of his long and extenfive experience in the principal branches of the ufeful and pleasing art of difcovering the properties and relations of bodies by wellimagined experiments.

ART. VII.