deavoured to obtain it. These circumftances have induced the anonymous Author of this work to publish his obfervations, which, he fays, were made during his refidence in thofe 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 thefe obfervations; 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 ufed; 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 fhort 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.

e

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 artift, 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 glass. To afcertain the degree of the charge, he ufes 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

Rr3

were

were proportional to the augmentation of its furface. In thefe 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 section of which, through its axis, contained nine fquare inches. With the 225 jars, he fplit 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 square 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, especially 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 obferved how many inches of each could be melted by the explofion of his battery; taking care, in all these experiments, to charge it to the fame degree, as afcertained by his electrometer, The refults were as follow:

Of filver, copper and brafs, not quite a quarter of an inch. These 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. According 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 thefe and fome other experiments of the fame kind, Dr. Van Marum concludes that, in melting metals, the electrical fluid 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 fubftances.

By these experiments on the fufibility of metals, Dr. Van Marum was induced to make trial of the comparative efficacy of lead, iron, brafs, and copper, as conductors to preserve 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, 3 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 first discharge. 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 explosion 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 resembled the painting of a very dark cloud. When

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fhorter

fhorter wires were calcined, the colours were more varied. A plate is given of the ftain made by the calcination of eight inches of this wire, in which the cloud appears variously fhaded with different tints of green, gray, and brown, in a manner of which no defeription can give an adequate idea.

On difcharging the battery through eight inches of tin wire, of an inch diameter, extended over a fheet of paper, a thick cloud of blue smoke arofe, in which many calcareous filaments were difcernible; at the fame time a great number of red hot globules of tin, falling upon the paper, were repeatedly thrown up again into the air, and continued thus to rebound from its furface for feveral feconds. The paper was marked with a yellowish clouded ftain, immediately under the wire, and with freaks or rays of the fame colour, iffuing from it in every direction: fome of thefe formed an uninterrupted line, others were made up of feparate fpots. In order to be certain that the colour of thefe ftreaks was not caufed by the paper being fcorched, the experiment was feveral times repeated, when a plate of glass, and a board covered with tin were placed to receive the globules. Thefe, however, were ftained exactly like the paper. On calcining five inches of the fame kind of wire, the red-hot globules were thrown obliquely to the height of four feet, which afforded an opportunity of obferving that each globule, in its courfe, diffused a matter like fmoke, which contihued to appear for a little while in the parabolic line defcribed by its flight, forming a track, in the air, of about half an inch in breadth.

From this phenomenon, Dr. VAN MARUM conjectures, that when the globules approach the paper on which they fall, the matter, iffuing from their lower part, ftrikes against its furface, and, being elastic, forces them upwards again by its reaction. The clouded ftain immediately under the wire, the Doctor attributes to the inftantaneous calcination of its furface, whereas the remainder of the metal is melted into globules, which, while they retain their glowing heat, continue to be fuperficially calcined, and, during the process, part with this calcareous vapour.

Phenomena, fomething fimilar to the above, were obferved on the calcination of a wire, of equal parts of tin and lead, eight inches long, and of an inch in diameter. This also was melted into red hot globules, which were repeatedly driven upwards again from the paper on which they fell, and marked it with ftreaks of the fame kind, but of a brown colour, edged with a yellow tinge. Some of thefe globules, though apparently not lefs hot, moved with lefs velocity than others, and were foon ftopped in their courfe, by their burning a hole in the paper. In this cafe, a yellow matter was feen to rife from their

furface,

furface, to the height of one or two lines, which extended itself to the width of a quarter of an inch. This matter continued, during five or fix feconds, to iffue from the globules, and formed, on their furface, a kind of efflorefcence, refembling the flowers of fulphur produced by the folfaterra. The globules, from which thefe calcareous flowers had iffued, were found to be entirely hollow, and to confift of only a thin fheil. When this mixed metal is calcined with a lefs charge of the battery, it leaves a ftain upon the paper, fomething timilar to that made by lead, and does not run into globules.

T

The Doctor has alfo given plates of the ftains made upon paper, by the calcination of iron, copper, brafs, filver, and gold. Thofe made by copper and brafs wires are remarkably beautiful, and are variegated with yellow, green, and a very bright brown. Eight inches of gold wire, of an inch in diameter, were, by the explosion, reduced to a purple fubftance, of which a part rofe like a thick fmoke, and the remainder, falling on the paper, left a ftain diverfified with different fhades of this colour. Gold, filver, and copper, cannot eafily be melted into globules; our author has once accidentally fucceeded in this; but it required a degree of electrical force fo very particular, that the medium between a charge, which only broke the wire into pieces, and one which entirely calcined it, could not be afcertained by the electrometer.

In accounting for thefe calcinations, Dr. VAN MARUM has adopted the theory of M. Lavoifier, to which he was converted from the Stahlian hypothefis, by attending upon the experiments of the French academicians in the year 1785. According to this theory, of which, in an Appendix to this work, he has given an excellent analysis, the metal, when, by the explofion, it has acquired a certain degree of heat, attracts, from the atmosphere, the principle of pure air (called, by M. Lavoifier, the oxiginous, or acidifying principle), in the fame manner as when it is caicined by fire; the variety of colours, with which it ftains the paper, is owing to the various proportions of this principle abforbed in different degrees of calcination; and that this variety is much greater in calcination by electricity, than in the fame operation by fire, may be accounted for, when we confider that, by the difcharge of the battery, various degrees of heat are inftantaneously acquired by different parts of the fame wire, which thus abforb the oxiginous principle in different proportions.

This chapter is clofed with an account, communicated to our author by M. Faujas de St. Fond, of the calcination of an iron bell wire by lightning, at Montelimar in Dauphiné, where the metal was reduced into a reddish brown duft, which was diffufed upon the wall, along which the wire had been conducted.

Though