have written on glass-making. Avicennal makes so complete a distinction between it and the magnet, that he treats of each in a particular section, though he says nothing of its employment in the glass-houses; but indeed as a physician he had no opportunity of doing so. Albertus Magnus, however, who lived a century later, Roger Bacon, Basilius Valentine, Camillus Leonardus, Biringoccio, Mercati, Neri and many others have spoken in the plainest terms of this application.

It is seen by the words quoted from different authors, that the name, which as far as I know occurs first in Albertus Magnus, was written in a great many different ways: magnesia, magnosia, magnasia, manganensis, mangadesum, and in French magalaise, méganaise, magnese. One might imagine that it is derived from magnet, partly on account of the similarity of the two substances, and partly on account of its supposed power to attract glass. Besides, its other name sidera seems to have a reference to the Greek word for iron. Mercati, however, deduces the term from mangonizare, because potters besmear their wares with this mineral; but I suspect that the name was common before that use of the substance was known. It is to be observed that to this word various other significations have been given. Sometimes it seems to denote common iron-stone, and sometimes pyrites. What the gold-makers understood by it will be best discovered by consulting the works of their followers. Braunstein also, the German name, the earliest mention of which occurs perhaps in the writings of Basilius Valentine, denoted at first every kind of ferruginous earth employed by the potters for painting. Thus Schwenkfeld gave the name of Braunstein and Braunfarbe to a kind of bloodstone3.

For a long time the manganese imported from Piedmont was in Germany accounted the best, and therefore was much sought after by the artists of Nuremberg. Afterwards, a kind brought from Perigord, a place in Guyenne, and named pierre de Périgueux, or lapis petracorius, was highly esteemed. Wallerius gives this as a peculiar species; and in

1 Canon Medicinæ, lib. ii. tract. 2, cap. 470, de Magnete; and cap. 472, de Magnesia.

2 In his book De Mineralibus, lib. ii. tract. 2, cap. 11.

> Stirpium et Fossilium Silesia Catalogus, Lipsia, 1600, 4to, p. 381,

my opinion he is right. Its distinguishing characters are, that it resembles a burnt coal or cinder; has a somewhat shining surface, and on the fracture appears to be finely striped and a little coloured. A piece which I have in my possession exhibits all these marks. This species has been mentioned by very few of the new mineralogists. Germany, however, for some centuries past has employed its own manganese, which even in the time of Biringoccio was sent as an article of commerce to Italy.

[The distinctness of the metal contained in the manganese of commerce from iron was first proved by the experiments of Pott in 1740, by Kaim and Winterl in 1770, and by Scheele and Bergman in 1774. Soon after this the metal itself was obtained in an isolated state by Gahn, who gave to it the name of magnesium, which term however was subsequently applied to the metal contained in magnesia, and the word manganese has been adopted to designate both the metal and the black ore. In addition to its application in the manufacture of glass, it is now very extensively used in the decomposition of common salt for the production of chlorine for bleaching. Some salts of the lower oxides of manganese have lately been used in calico-printing as a source of brown colours.]

PRINCE RUPERT'S DROPS. LACRYMÆ VITREÆ.

Ir is more than probable that these drops, and the singular property which they possess, have been known at the glasshouses since time immemorial. All glass, when suddenly cooled, becomes brittle, and breaks on the least scratch. On this account, as far back as the history of the art can be traced, a cooling furnace was always constructed close to the fusing furnace. A drop of fused glass falling into water!

1 It is not always necessary that the water should be cold; these drops will be formed also in warm water, as well as in every other fluid, and even in melted wax. See Redi's experiments in Miscellan. Naturæ Curios. anni secundi, 1671, p. 426. They succeed best with green glass, yet 【

VOL. II.

R

might easily have given rise to the invention of these drops; at any rate this might have been the case in rubbing off what is called the navel'. It is however certain that they were not known to experimental philosophers till the middle of the seventeenth century. Their withstanding great force applied at the thick end, and even blows; and on the other hand, bursting into the finest dust when the smallest fragment is broken off from the thin end, are properties so peculiar that they must excite the curiosity of philosophers, and induce them to examine these effects, especially at a time when mankind in general exert themselves with the greatest zeal to become better acquainted with the phænomena of natural bodies. On this account they have been noticed in almost every introduction to experimental philosophy. To determine the time then in which they were first made known, seems to be attended with little difficulty; but it still remains doubtful by whom and in what country.

It appears certain that the first experiments were made by philosophers with these drops in the year 1656. Monconys, who travelled at that period, was present when such experiments were made at Paris, before a learned society, which assembled at the house of Mommor, the well-known patron of Gassendi; and the same year he saw similar experiments made by several scientific persons at London. He tells us expressly that Chanut, the Swedish resident, procured glass drops for the first Parisian experiments, and that these drops were brought from Holland.

It appears, therefore, that the first glass drops were made in Holland; yet Montanari, who was professor of mathematics at Bologna, says that the first were not made by the Dutch, but by the Swedes. The grounds, however, on which he rests his assertion are exceedingly weak. Because a Swedish resident procured those used for the first experiments, it does not follow that they were made at Swedish glass-houses,

have in my possession some of white glass, which in friability are not inferior to those of green.

1 The navel, in German nabel, is that piece of glass which remains adhering to the pipe when any article has been blown, and which the workman must rub off. These navels, however, are seldom in so fluid a state as to form drops.

2 Journal des Voyages de M. Monconys, Lyon, 1666, 4to, ii. p. 162.

especially as it is positively said that they were brought from Holland. It was indeed stated so early as 1661, by Henry Regius or Van Roy, professor at Utrecht, that these glass drops came from Sweden; but may not this have been a lapse of memory, occasioned by the circumstance that the first drops used by the natural philosophers of Paris were procured by a Swedish resident.

Monconys, whose relation indeed bears evident marks of great haste as well as credulity, calls Chanut Résident de Suède, and seems to have considered him as a Swedish resident at the French court; an opinion in which he has been followed by many literary men. But Pierre Chanut was French resident at Stockholm, and at that time so well-known that Monconys could hardly be unacquainted with his quality. He was resident from the year 1645 to 1649; and he was afterwards envoy for adjusting the disputes between Sweden and Poland, which were to be settled at Lubec. He is often mentioned in Puffendorf's book De Rebus Suecicis, and the printed account of his missions and negociations contain important materials towards a history of queen Christina, with whom he was a great favourite. He superintended the funeral of Descartes, who was interred with great honour. He was born in 1601; but with the time of his death I am unacquainted. He was celebrated as a man of great learning, and particularly an able mathematician; and it is neither improbable nor even impossible that he may have sent the first glass drops to Paris from Sweden; but why does Monconys add that they were brought from Holland?

It deserves to be mentioned, that about fifteen years before, that is in 1641, the first glass-houses were established in Sweden, and in all probability by Germans. It is possible that when the blowing of glass was first seen, glass drops may have excited an attention which they had not met with in Germany, where no one expected anything new in glasshouses, which were there common and had long been established. It can nevertheless be proved that they were known to our glass-blowers at a much earlier period.

In 1695, John Christian Schulenburg, subrector of the cathedral school of Bremen, published there a German Dissertation on glass drops and their properties, in which he says that he was informed by glass-makers worthy of credit, that

these drops had been made more than seventy years before at the Mecklenburg glass-houses, that is to say, about the year 1625.

Samuel Reyher, professor at Kiel, says that Henry Sievers, teacher of mathematics in the gymnasium of Hamburg, had assured him that such glass drops were given to his father by a glass-maker so early as the year 1637; and that his father had exhibited them in a company of friends, who were much astonished at their effects. Reyher adds, that he himself had seen at Leyden, in 1656, the first of these glass drops, which had been made at Amsterdam, where he afterwards purchased some of the same kind; but in 1666 he procured for a very small sum a great many of them from the glass-houses in the neighbourhood of Kiel. It is worthy of remark, that Huet', who paid considerable attention to the history of inventions, says that the first glass drops, which he had seen also in the society held at the house of Mommor, were brought to France from Germany. According to Anthony Le Grand they came from Prussia 2.

The first glass drops were brought to England by the wellknown Prince Rupert, third son of the elector Palatine, Frederic V., and the princess Elizabeth, daughter of James I.; and experiments, described by Rupert Moray, were made with them in 1661 by command of his majesty. This is expressly stated by Merrets; and therefore what some English writers have supposed, that Prince Rupert himself was the inventor, is entirely erroneous. The services which he rendered to the useful arts were too great and too numerous to be either lessened or increased by such trifles.

I shall take this opportunity of remarking, that those small glasses hermetically sealed and containing a drop of water, which when placed on hot coals burst with a loud report, and therefore are called in German knallgläser, fulminating glasses, were known before 1665. Hooke speaks of them in his Micrographia printed in that year, and they were mentioned by 1 Commentarius de rebus ad eum pertinentibus, Lips. 1719. 2 Historia Naturalis. Edit. secunda, Londini 1680, 4to, p. 37. 3 In his Observations on Neri Ars Vitraria, Amstel. 1668, 12mo. 4 This is said, for example, by Grainger in his Biographical History o England. London, 1769, vol. ii. part 2, p. 407.

5 This book was only once printed, but the title-page has the date 1667. See Biographia Britannica. iv. p. 2654.