for the excellent work he had dedicated to me; but at the fame time I informed him, that, fenfible to the good wishes expreffed in his Dedication, I fhould be ungrateful if I did not, for his own fake, with that he had entirely altered the style of it.'

M. Suhm's letters are much inferior to thofe of the Prince, and are fo full of adulation, we had almost faid adoration, that we wonder they did not draw a ferious reprimand from his Highnefs, who indeed checks him frequently on this account. His affection was no doubt fincere and praife-worthy, but his expreffion of it is as ridiculous as the love ditty of a whining knight in romance, and is void of that fober dignity which fhould characterise the friendship of a man of fenfe. His tranfports and extafies are fo much in the fuperlative degree, and fo repeatedly expreffed, that we were quite cloyed and difgufted with them.

The fubjects to which thefe letters are confined are not the moft interefting and entertaining. They contain no political or hiftorical anecdotes, and are remarkably filent concerning the court of Berlin. This was prudent, confidering the Prince's difagreeable fituation at that time. His Royal Highness, who entertained rather an unreasonable prejudice against the German, and in favour of the French language, had engaged M. Suhm to tranflate Wolf's metaphyfics, and to fend him the tranflation, fheet by fheet, inclofed in his letters. An account of the progrefs of this work, and a few general encomiums on Wolf, are all the information contained in the firft thirty-fix letters; after which we find that M. Suhm was appointed by the Elector to fucceed the Count de Linar as Envoy Extraordinary to the Court of Petersburgh. The remainder of the correfpondence relates to certain fums of money which the Prince fecretly borrowed from the Empress Anne Iwanowna of Ruffia, and from the Duke of Courland, formerly Count Biran, her favourite. Among thefe letters, there is one in which his Highness mentions his having been accused, to the King, of irreligion, and adds, 'You know that an acculation of this kind is the laft refuge of calumny; after this, nothing further can be faid. The King took fire; I kept myself close; my regiment did wonders; and their dexterity in handling their arms, a little flour fcattered on the foldiers heads, men above fix feet high, together with a great many recruits, were arguments more powerful than those of my accufers. Every thing is now quiet, and I hear nothing more about religion, my perfecutors, or my regiment.'

On the Prince's acceffion to the throne, one of his first cares was to perfuade M. Suhm to refign his connections with the Court of Drefden, and to fix at Berlin. The latter complied with this cordial invitation, but, on his journey, died at Warfaw; and his laft letter, dated from this city, is the dying man's pathetic

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pathetic recommendation of his fifter and his children to his royal friend. This letter is admirably written: it flows immediately from the heart; and it gives us an affecting view of the fentiments of the Chriftian, the philofopher, the father, and the friend, in thefe awful circumftances; and affords a ftriking inftance of the vanity of our most probable fchemes of worldly happineís.

This correfpondence is followed by a few fhort letters from the King to the Countess de Samas, who was at the head of the Queen's household, written between the years 1760 and 1763. They are pleafant trifles. We have attempted to tranflate one of them, which fhews the King's mind to have been perfectly at ease amid the horrors of war, and fuperior to the influence of external circumftances.

Newftadt, November 11, 1760.

I am punctual in anfwering, and eager to oblige you. Perfons of the fame age agree wonderfully. I have given up fuppers thefe four years, as incompatible with the bufinefs I am forced to carry on; and, on marching days, my dinner is only a dish of chocolate. We have been running like madmen, quite elated with victory, to fee whether we could drive the Auftrians from Drefden; but they Jaughed at us from the tops of their mountains. I returned like a difappointed child, to hide my vexation in one of the most curfed villages of Saxony. We must now drive Meffieurs Les Cercles out of Freyberg and Chemnitz, in order to get fomething to eat, and a place to fleep in.

This is, I fwear, fuch a dog's life, as no one, except Don Quixotte, ever led but myself. All this buttle, all this confufion, which feems to be without end, has made me fuch an old fellow, that you will hardly know me again. The hair on the right fide of my head is grown quite grey; my teeth break, and fall out; my face is as full of wrinkles as the furbelow of a petticoat, and my back arched like a monk's of La Trappe. I give you notice of all this, that, if we fhould meet again in fkin and bone, you may not be shocked at my figure. Nothing belonging to me remains unaltered, except my heart, which, as long as I breathe, will retain its fentiments of affection and tender friendship for my good Mama. Adieu.'

ART. XI.

Obfervations fur le Commerce de la Mer Noire, &c. i. e. Observations on the Commerce of the Black Sea, and the adjacent Countries. To which are added, Remarks on the Trade of Candia and Smyrna. 12mo. Amiterdam. 1787.

HEcommerce of the Euxine was formerly engroffed by

TH the Turks, who would not fuffer the veffels of any

European power to navigate this fea; but fince the year 1783, the Rulians and Imperialifts have enjoyed this privilege, and the French and Dutch Ambafiadors at the Porte, have alfo en

deavoured

deavoured to obtain it. Thefe circumftances have induced the anonymous Author of this work to publifh his obfervations, which, he fays, were made during his refidence in those countries from the year 1759 to 1762. From the preface he appears to be a fugitive from France, refiding in Amfterdam. He accufes Louis Antoine Duvalz, a French adventurer, of having ftolen a copy of these observations; and complains that another work of his, of what kind we know not, was furreptitiously carried off to Paris, and being there publifhed, was afcribed to a certain well-known magiftrate, whofe name however he does not mention. If all this be true, he has been hardly used; but, as he has not thought fit to acquaint the Public with his name, we know not what credit to give to his affertions. The Obfervations confift of a short commercial defcription of the Crimea, and a very minute account of the articles of trade there, in various parts of Turkey, and in the Levant; together with a project for eftablishing a commercial company at Conftantinople, and directions concerning the manner of carrying on business in those countries.

ART. XII.

Eerfte Vervolg der Proefneemingen gedaan met Teylers Electrizeer Machine. i. e. Continuation of Experiments performed with the Electrical Machine in Teyler's Museum in Haarlem. By MARTINUS VAN MARUM, M. D. Librarian and Director of this Inftitution, Correfponding Member of the Royal Academy of Sciences at Paris, and Member of the Philofophical Societies of Haarlem, Rotterdam, Vliffing, and Utrecht. 4to. Haarlem.

1785.

TH

HIS publication has been unavoidably delayed on account of the coloured plates, which were neceffary to give an adequate idea of fome of the phenomena. These plates were executed by M. Sepp, of Amfterdam, an artist, whofe accuracy and excellence, in this particular branch, Dr. Van Marum hopes will compenfate for the delay occafioned by employing him.

The battery, with which the former experiments were made (fee Appendix to our lxxiii. volume), confifted of 135 fquare feet of coated glass; but the Doctor, thinking that the machine was capable of charging a larger furface, had added to it go jars, each of the fame fize with the former; fo that his grand battery is now a fquare of 15 jars every way, and contains 225 fquare feet of coated glafs. To afcertain the degree of the charge, he uses the Electrometer invented by M. Brook, which is fixed in the center of the battery, at the height of four feet above the knobs of the jars.

His first object was to try whether this battery could be fully charged by the machine, and whether its increase of power

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were

were proportional to the augmentation of its furface. In these refpects, his expectations were fully answered. The former battery discharged itself over the uncoated part of the jars, after 96 revolutions; and the prefent did the fame after 160 turns of the machine. With the former battery, the Doctor had split a cylinder of box, three inches in diameter, and three inches in length, the fection of which, through its axis, contained nine fquare inches. With the 225 jars, he split a fimilar cylinder, four inches in diameter, and four inches in height, the fection of which was fixteen fquare inches. He found that to split a fquare inch of this wood in the fame direction, required a force equal to 615 pounds, and hence calculates that the power of this explofion was not lefs than 9840 pounds.

The apparent refemblance between the effects of electricity, and of fire, efpecially in melting metals, has led many to fuppofe that they act on bodies in a fimilar manner. In order to examine whether this fuppofition be juft, Dr. Van Marum caused wires of different metals to be drawn through the fame hole, of one thirty-eighth part of an inch in diameter, and ob. ferved how many inches of each could be melted by the explofion of his battery; taking care, in all thefe experiments, to charge it to the fame degree, as afcertained by his electrometer. The refults were as follow:

Of lead he melted

Of tin

Of iron

Of gold

120 inches,

120

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Of filver, copper and brafs, not quite a quarter of an inch. Thefe feveral lengths of wire, of the fame diameter, melted by equal explosions, indicate, according to our author, the degree in which each metal is fufible by the electrical discharge; and, if these be compared with the fufibility of the fame metals by fire, a very confiderable difference will be obferved. cording to the experiments of the academicians of Dijon, to melt tin required a heat of 172 degrees of Reaumur's ther

Thus tin and lead appear to be equally fufible by electricity, but not by fire and iron, which, by fire, is lefs fufible than gold, is much more fo by the electrical explofion. From these and fome other experiments of the fame kind, Dr. Van Marum concludes that, in melting metals, the electrical Auid acts upon them in a manner very different from the action of fire, and

that

that the fuppofed analogy between these two powerful agents cannot be proved, either from the fufion of metals, or the ignition of combuftible substances.

By thefe experiments on the fufibility of metals, Dr. Van Marum was induced to make trial of the comparative efficacy of lead, iron, brass, and copper, as conductors to preferve buildings from lightning. In this refpect, he found that a leaden conductor ought to be four times the fize of one of iron, in order to be equal in point of fafety. He has alfo fully proved the fuperiority of rods to chains, and of copper to iron, for this important use.

When iron wire is melted by the explofion of the battery, the red-hot globules are thrown to a very confiderable diftance, fometimes to that of thirty feet: this the Doctor juftly afcribes to the lateral force exerted by the electrical fluid. It is however remarkable that, the thicker the wire is, which is melted, the further are the globules difperfed; but this is accounted for, by obferving, that the globules, formed by the fufion of thinner wires, being fmaller, are lefs able to overcome the refiftance of the air, and are therefore fooner stopped in their motion.

Two pieces of iron wire being tied together, the fufion extended no further, than from the end connected with the infide coating of the jars, to the knot; though wire of the fame length and thickness, when in one continued piece, had been entirely melted by an equal explosion.

When a wire was too long to be melted by the discharge of the battery, it was fometimes broken into feveral pieces, the extremities of which bore evident marks of fufion; and the effect of electricity, in fhortening wire, was very fenfible in an experiment made with 18 inches of iron wire, of an inch in diameter, which, by one difcharge, loft a quarter of an inch of its length. An explofion of this battery through very small wires, of nearly the greatest length that could be melted by it, did not entirely difcharge the jars. On tranfmitting the charge through 50 feet of iron wire, of of an inch diameter, the Doctor found that the refiduum was fufficient to melt two feet of the fame wire; but this refiduum was much lefs, when the wire was of too great a length to be melted by the firft difcharge. After an explosion of the battery through 180 feet of iron wire, of equal diameter with the former, the refiduum was discharged through 12 inches of the fame wire, which it did not melt, but only blued.

Twenty-four inches of leaden wire, of an inch in diameter, were entirely calcined by an explofion of this battery; the greater part of the lead rofe in a thick smoke, the remainder was ftruck down upon a paper laid beneath it, where it formed a ftain, which refembled the painting of a very dark cloud. When

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fhorter