fused at the glass-houses1. But by that term he seems to understand a kind of marble, according to the opinion of Isidorus, by whom the word is repeated. As a calcareous earth it was perhaps added to promote the fusion of the sand. Camillus Leonardus, however, considered the Alabandicus as manganese2.

It is not improbable that the ancients employed manganese, if not for glazing, at any rate for painting their pottery or earthenware, as soon as they became acquainted at the glass-houses with its susceptibility of being converted into a coloured vitreous mass.

But this is far from being proved, though count Caylus, Genssane and others positively assert that the so-called Etruscan vases and lamps were painted with the same manganese that we use for our earthen-ware.

Those who attempt to trace out the history of the arts must be very cautious not to admit, without sufficient proof, that what the ancients accomplished was effected by the same means as those employed by us for the same purpose. This, in some cases, may be true; but in many others false. Thus, they made a beautiful kind of blue and red glass, without being acquainted with our cobalt and mineral purple; and they performed very long sea voyages without our compass. It is the duty of the historian either to point out the means which the ancients employed, whether they were the same or not as those used at present, or to acknowledge that their processes are unknown to us. Those who invariably follow this rule will sometimes discover that, in ancient times, men were able to accomplish the same objects and to produce the 1 Plin. xxxvi. 8, § 13, p. 735.

2 Speculum Lapidum, Parisiis, 1610, 8vo, p. 71. It may not be superfluous here to remark, that this Alabandicus of Pliny must not, as is often the case, be confounded with the precious stone to which he gives the same name, lib. xxxvii. cap. 8. The name properly denotes only a stone from Alabanda in Caria. It occurs, but much corrupted, as the name of a costly stone, in writings of the middle ages. See in Du Cange Alamandinæ, Alavandinæ, Almandinæ ; and even in our period so fertile in names, a stone which is sometimes classed with the ruby and sometimes with the garnet, and which is sometimes said to have an affinity to the topaz and hyacinth, is called Alamandine and Alabandiken. See Brückman on Precious Stones, who in the second continuation, p. 64, deduces the word from Allemands, without recollecting the proper derivation, which he gives himself, i. p. 89, according to Pliny.

same effects, by means totally different from those used at present; and then the question will sometimes arise, Which of the means, the old or the new, are the cheapest, the most convenient, and the surest? This leads to technological problems, the solution of which, notwithstanding the great superiority we possess in those auxiliaries of the arts, natural history, chemistry, &c., is impossible. I have indulged in these observations, in mentioning the celebrated Caylus, because I well know that he has often erred in not attending to them. I acknowledge and respect the service of this eminent man; but I am convinced that by the boldness of his assertions he acquired greater confidence and more celebrity than he deserved.

The colours on the Etruscan vases have a resemblance indeed to those on our stone-ware, but it is also true that they might be produced by oxide of iron.

The substances used by the ancient potters can be determined only by the testimony of the ancients or by experiments; but the former is not to be found; and the latter have never been made, though they would not be difficult to any chemist who might choose to sacrifice a few vessels of that kind.

The question how the use of manganese was first found out, occurred even to Pliny; and his opinion on that subject deserves to be quoted, especially as it was long considered as true by Albertus Magnus, Caneparius, and many later writers. To understand it one must know that it was at first believed that the magnet, as it attracts iron, could attract other bodies also; and it was conjectured that other minerals might possess a similar property. Some imagined that they had found magnets for gold and silver. In the oldest times men had so erroneous an opinion of the art of glass-making, that they conceived that glass was obtained from sand, as metal from its ore; and Pliny thinks that they then conjectured that a magnet could attract glass as well as it does iron. Now as manganese, on account of its similarity, was considered to be a magnet, it was consequently subjected to experiments, which gave rise to the beneficial discovery that it renders glass colourless.

This use of it then has been retained through every age to the present time, and it is mentioned by all those authors who

have written on glass-making. Avicenna1 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 2, 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.

3 Stirpium et Fossilium Silesiæ Catalogus, Lipsiæ, 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.

It 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 water1

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 I

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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.