LITMIR.BIZ

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      After this period the tourmaline must have been very scarce in Europe; for when Muschenbroek made his well-known experiments with the loadstone, and spared no labour to carry them to the utmost extent, he was not acquainted with the nature of the tourmaline, which, according to the account given of it by the Academy at Paris, he considered as a magnet, as he himself says in the preface to his first dissertation, published in 1724.

      About the year 1740 however some German naturalists made experiments with this stone, in order to discover the real cause of its attractive property. These may be seen, under the article Trip, in the well-known Dictionary of Natural History which is often printed with Hübner’s preface; but I do not know to whom the honour belongs of having first investigated the properties of this stone. As the above dictionary is common, I shall give here only a very short extract from it: – “This stone was brought to Holland by some persons who had travelled in India, from the island of Ceylon, where it is found pretty frequently among the fine sand near Columbo, and sold to the German Jews. These caused it to be cut thinner, and the price of it soon rose to eight and ten Dutch florins. It has been since much dearer; but at present it is cheaper. It attracts not only ashes, but also metallic calces: it however attracts more easily and with greater force those which have been formed by means of sal-ammoniac, or the spirit of that salt. It acquires its attractive power only after it has been moderately heated; for when cold or heated to a greater degree it produces no effect, which the author ascribes to its being united with martial sulphur. The chrysolites and other precious stones of the island do not possess the same property.” As the author quotes the Laboratorium Zeylonicum, I consulted it, but found no information in it respecting the tourmaline. The first person who thought of explaining the property of the tourmaline by electricity was the great Linnæus, who in the preface to his Flora Zeylanica222, where he enumerates the productions of the island, calls it the electrical stone; but at that time, as he himself afterwards told me, he had not seen it.

      What Linnæus only conjectured, Æpinus proved at Berlin in 1757 by accurate observation and experiments, when endeavouring with Wilke to investigate the secret of negative and positive electricity. The history of their discoveries I shall here omit, as a better account of them than I could give has been published in the Transactions of the Swedish Academy by Wilke.

      [The discovery by Huygens, in 1678, of the polarization of light by double refraction, laid the foundation of a much more important application of the tourmaline; for MM. Biot and Seebeck, in their subsequent experiments, discovered that certain yellowish tourmalines, that is, those which are yellowish by refracted light, possessed the remarkable property of absorbing or checking one of the rays of a beam of polarized light, and transmitting the others. This discovery led to the use of tourmalines in most experiments which were subsequently made with polarized light. For this purpose, the tourmaline, which generally crystallizes in the form of a long prism, is cut lengthwise, that is, parallel to the axis of the prism, into plates about the 30th of an inch thick.

      The invention of Mr. Nichol of a method of destroying one of the rays of a polarized beam in a crystal of calcareous spar, has however in later times entirely replaced the use of the tourmaline in optical science, the colour of the tourmaline being a disadvantage which is entirely removed in the use of Nichol’s prism223.]

      SPEAKING-TRUMPET

      Instruments by which the voice could be so strengthened as to be heard at a much greater distance than would otherwise have been possible, were known in the earliest ages; for of all musical instruments, wind instruments were first invented, and their use in war to give the signal of battle, we find mentioned in Job224. It had been remarked, even in Pliny’s time, that the least touch of a beam of wood could be heard when the ear was applied to the other end225. It was known likewise that the larger trumpets emitted a louder and stronger sound. The Grecians had a wind instrument with the bellowing noise of which the people who were placed to guard the vineyards frightened away the wild animals226. All these wind instruments however were little in comparison with the monstrous trumpets of the ancient Chinese, a kind of speaking-trumpets, or instruments by which words could not only be heard at the greatest distance possible, but could be also understood227. This invention belongs to the 17th century, though some think that traces of it are to be found among the ancient Grecians.

      Kircher, as far as I have been able to learn, was the first person who made known, from a very ancient manuscript of Aristotle, De Secretis ad Alexandrum Magnum, preserved in the Vatican, that Alexander had a prodigious large horn with which he could assemble his army at the distance of a hundred stadia, or eight Italian miles. It was, according to the manuscript, five cubits in diameter; and Kircher, who gives a figure of it, which he says he found in the manuscript, thinks that, on account of its size, it must have been suspended from a beam by a ring. This horn has by many been considered as the oldest speaking-trumpet228, but in my opinion without reason. Aristotelis Secretum Secretorum ad Alexandrum Magnum I have never had an opportunity to see. It appears to have been printed only once, and is, like all the other works ascribed to that philosopher, extremely scarce; for they have all had the fate of being little regarded after it became the unanimous opinion of the learned that they were forged. These works, however, are old; some of them indeed very old: and, if some one would take the trouble to fix their antiquity, they might be used with advantage on many occasions. Morhof had in his possession the edition of that book published by Alexander Achillinus, a physician at Bologna, in 1516, which is a Latin translation from the Arabic229. If we compare what is said there and by Kircher, we may make the following conclusion: —

      In the first place, it is certain that the book itself, as well as the whole account, is not the production of Aristotle, for in all the writers who relate the actions of Alexander we do not find the least mention of such a horn. Secondly, it is not expressly said in that work that Alexander spoke through this horn, but only that he assembled his soldiers by it, which in past times was done by the sound of a trumpet, and at present is done both by trumpets and drums. It appears also that the author of the book, perhaps an Arabian, intended to give the reader an idea of a horn that had an uncommonly strong and loud sound. Thirdly, Kircher’s account and figure of the horn do not agree with that which Morhof found in the edition of Achillinus230. Lastly, none of these descriptions are such that an instrument to serve as a speaking-trumpet could be constructed from them.

      Wolf and other mathematicians are of opinion that the most advantageous form of a speaking-trumpet would be found with more certainty by experience than by theory. It may then be asked, whether any one ever caused such an instrument to be made from these descriptions. Kircher, who attempted things much more improbable, says he never tried it. Duhamel however relates that a Frenchman tried it, and discovered the real instrument231; but this information is of little weight, as it is much to be doubted that this Frenchman caused it to be made sufficiently exact according to the ancient description. I am as little acquainted with Bettini as Morhof; but I suspect that Duhamel meant Mar. Bettini, who, without making the smallest mention of Alexander’s horn, proposes only a tube, the one end of which should be applied to the mouth of a person who speaks, and the other to the ear of one who is dull of hearing232. This was rather an ear-trumpet than a speaking-trumpet, and it is certain that the former was invented before the latter.

      What we read in Porta, and what many think alludes to a speaking-trumpet, alludes evidently to an ear-trumpet only. That author infers, very justly, from the form of the ear, and particularly from that of the ears of those animals which are quick of hearing, that to hear at a distance one must apply to the ear a kind of wide funnel, as people to strengthen the sight use spectacles233. He asserts also, with equal truth, that one, through a long tube, can convey a whisper to the ear of another person at a very great distance Скачать книгу