49

c. Magnetic Activity of the Earth in its three Manifestations of Force-Intensity, Inclination, and Variation.-Points (called the Magnetic Poles), in which the Inclination is 90°. - Curves on which no Inclination is observed (Magnetic Equator). The Four different Maxima of Intensity.Curve of weakest Intensity.-Extraordinary Disturbances of the Declination (Magnetic Storms).-Polar Light. (Extension of the Picture of Nature, Cosmos, vol. i. pp. 169 -197, vol. ii. pp. 717-720, and vol. iv. pp. 394-398.)

The magnetic constitution of our planet can only be deduced from the many and various manifestations of terrestrial force in as far as it presents measureable relations in space and time. These manifestations have the peculiar property of exhibiting perpetual variability of phenomena to a much higher degree even than the temperature, gaseous admixture, and electrical tension of the lower strata of the atmosphere. Such a constant change in the nearly allied magnetic and electrical conditions of matter moreover essentially distinguishes the phenomena of electro-magnetism from those which are influenced by the primitive fundamental force of matter-its molecular attraction and the attraction of masses at definite distances. To establish laws in that which is ever varying, is however the highest object of every investigation of a physical force. Although it has been shown by the labours of Coulomb and Arago that the electro-magnetic process may be excited in the most various substances, it has nevertheless been proved by Faraday's brilliant discovery of diamagnetism, (by the differences of the direction of the axes, whether they incline north and south, or east and west,) that the heterogeneity of matter exerts an influence distinct from the attraction of masses. Oxygen gas, when inclosed in a thin glass tube, will show itself under the action of a magnet to be paramagnetic, inclining north and south like iron; and while nitrogen, hydrogen, and carbonic acid gases remain unaffected, phosphorus, leather, and wood show themselves to be diamagnetic, and arrange themselves equatorially from east to west.

VOL. V.

E

The ancient Greeks and Romans were acquainted with the adhesion of iron to the magnet, attraction and repulsion, and the transmission of the attracting action through brass vessels as well as through rings, which were strung together in a chain-like form, as long as one of the rings was kept in contact with the magnet; and they were likewise acquainted with the non-attraction of wood and of all metals excepting iron. The force of polarity, which the magnet is able to impart to a moveable body susceptible of its influence, was entirely unknown to the Western nations (Phoenicians, Tuscans, Greeks, and Romans). The first notice which we meet with among the nations of Western Europe of the knowledge of this force of polarity, which has exerted so important an influence on the improvement and extension of navigation, and which, from its utilitarian value has led so continuously to the inquiry after one universally diffused, although previously unobserved force of nature, does not date farther back than the 11th and 12th centuries. In the history and enumeration of the principal epochs of a physical contemplation of the universe, it has been found necessary to divide into several sections, and to notice, the sources from which we derive our knowledge of that which we have here summarily arranged under one common point of view.53

We find that the application amongst the Chinese of the directive power of the magnet, or the use of the north and south direction of magnetic needles floating on the surface of water, dates to an epoch which is probably more ancient than the Doric migration and the return of the Heraclidæ into the Peloponnesus. It seems, moreover, very striking that the use of the south direction of the needle should have been first applied in Eastern Asia not to navigation but to land travelling. In the anterior part of the magnetic waggon a freely floating needle moved the arm and band of a small figure, which pointed towards the south. An apparatus of this kind (called fse-nan, indicator of the south,) was pre

52 The principal passage referring to the magnetic chain of rings occurs in Plato's Ion. p. 533, D.E ed. Steph. Mention has been made of this transmission of the attracting action not only by Pliny (xxxiv, 14) and Lucretius (vi, 910), but also by Augustine (de civitate Dei, xx, 4) and Philo (de Mundi opificio, p. 32 D ed. 1691).

53 Cosmos, vol. i, p. 182; vol. ii, p. 623.

sented during the dynasty of the Tscheu, 1100 years before our era, to the ambassadors of Tonquin and Cochin-China, to guide them over the vast plains, which they would have to cross in their homeward journey. The magnetic waggon was used as late as the 15th century of our era. 54 Several of these waggons were carefully preserved in the imperial palace and were employed in the building of Buddhist monasteries in fixing the points towards which the main sides of the edifice should be directed. The frequent application of magnetic apparatus gradually led the more intelligent of the people to physical considerations regarding the nature of magnetic phenomena. The Chinese eulogist of the magnetic needle, Kuopho (a writer of the age of Constantine the Great), compares, as I have already elsewhere remarked, the attractive force of the magnet with that of rubbed amber. This force, according to him, is "like a breath of wind which mysteriously breathes through these two bodies, and has the property of thoroughly permeating them with the rapidity of an arrow." The symbolical expression of "breath of wind" reminds us of the equally symbolical designation of soul, which in Grecian antiquity was applied by Thales, the founder of the Ionian School, to both these attracting substances; soul signifying here the inner principle of the moving agent.

55

54 Humboldt, Asic Centrale, t. i, p. xl-xlii, and Examen Crit. de Hist. de la Géographie, t. iii, p. 35. Eduard Biot, who has extended and confirmed by his own careful and bibliographical studies, and with the assistance of my learned friend Stanislas Julien, the investigations made by Klaproth in reference to the epoch at which the magnetic needle was first used in China, adduces an old tradition, according to which the magnetic waggon was already in use in the reign of the Emperor Hoang-ti. No allusion to this tradition can, however, be found in any writers prior to the early Christian ages. This celebrated monarch is presumed to have lived 2600 years before our era (that is to say, 1000 years before the expulsion of the Hyksos from Egypt). Ed. Biot sur la direction de l'aiguille aimantée en Chine in the Comptes rendus de l'Acad. des Sciences, t. xix, 1844, p. 822.

55 Cosmos, vol. i, p. 182. Aristotle (de Anima, i, 2) speaks only of the animation of the magnet as of an opinion that originated with Thales. Diogenes Laertius interprets this statement as applying also distinctly to amber, for he says, "Aristotle and Hippias maintain as to the doctrine enounced by Thales." The sophist Hippias of Elis, who flattered himself that he possessed universal knowledge, occupied himself with physical science and with the most ancient traditions of

As the excessive mobility of the floating Chinese needles rendered it difficult to observe and note down the indications which they afforded, another arrangement was adopted in their place as early as the 12th century of our era, in which the needle that was freely suspended in the air was attached to a fine cotton or silken thread exactly in the same manner as Coulomb's suspension which was first used by William Gilbert in Western Europe. By means of this more perfect apparatus, the Chinese as early as the beginning of the 12th century determined the amount of the western variation, which in that portion of Asia seems only to undergo very inconsiderable and slow changes. From its use on land, the compass was finally adapted to maritime purposes, and under the dynasty of Tsin, in the 4th century of our era, Chinese vessels under the guidance of the compass visited Indian ports and the eastern coast of Africa.

56

Fully 200 years earlier, under the reign of Marcus Aurelius Antoninus, who is called An-tun by the writers of the dynasty of Han, Roman legates came by sea by way of Tonquin to China. The application of the magnetic needle to European navigation was however not owing to so transient a source of intercourse, for it was not until its use had become general thoughout the whole of the Indian Ocean, along the shores of Persia and Arabia, that it was introduced into the West in the 12th century, either directly through the influence of the Arabs or through the agency of the Crusaders, who since 1096 had been brought in contact with Egypt and the true Oriental regions. In historical investigations of this nature, we can only determine with certainty the physiological school. "The attracting breath," which, according to the Chinese physicist, Kuopho, "permeates both the magnet and amber," reminds us, according to Buschmann's investigations into the Mexican language, of the aztec name of the magnet tlaihioanani tetl, signifying "the stone which attracts by its breath" (from ihiotl, breath, and ana, to draw or attract).

56 The remarks which Klaproth has extracted from the Penthsaoyan regarding this singular apparatus are given more fully in the Mungkhi-pi-than, Comptes rendus, t. xix, p. 365. We may here ask why, in this latter treatise, as well as in a Chinese book on plants, it is stated that the cypress turns towards the west, and, more generally, that the magnetic needle points towards the south? Does this imply a more luxuriant development of the branches on the side nearest the sun, or in consequence of the direction of the prevalent winds?

those epochs, which must be considered as the latest limits beyond which it would be impossible for us to urge our inquiries. In the politico-satirical poem of Guyot of Provins, the mariner's compass is spoken of (1199) as an instrument that had been long known to the Christian world; and this is also the case in the description of Palestine which we owe to the Bishop of Ptolemais, Jaques de Vitry, and which was completed between the years 1204 and 1215. Guided by the magnetic needle the Catalans sailed along the northern islands of Scotland as well as along the western shores of tropical Africa, the Basques ventured forth in search of the whale, and the Northmen made their way to the Azores (the Bracir islands of Picigano). The Spanish Leyes de las Partidas (del sabio Rey Don Alonso el nono), belonging to the first half of the 13th century, extolled the magnetic needle 66 as the true mediatrix (medianera) between the magnetic stone (la piedra) and the north star.' Gilbert also, in his celebrated work De Magnete Physiologia Nova, speaks of the mariner's compass as a Chinese invention, although he inconsiderately adds, that Marco Polo "qui apud Chinas artem pyxidis didicit," first brought it to Italy. As, however, Marco Polo began his travels in 1271 and returned in 1295, it is evident from the testimony of Guyot of Provins and Jaques de Vitry, that the compass was at all events used in European seas from 60 to 70 years before Marco Polo set forth on his journeyings. The designations zohron and aphron, which Vincent of Beauvais applied in his Mirror of Nature to the southern and northern ends of the magnetic needle (1254), seem to indicate that it was through Arabian pilots that Europeans became possessed of the Chinese compass. These designations point to the same learned and industrious nation of the Asiatic peninsula whose language too often vainly appeals to us in our celestial maps and globes.

From the remarks which I have already made, there can scarcely be a doubt that the general application of the magnetic needle by Europeans to oceanic navigation as early as the 12th century, and perhaps even earlier in individual cases, originally proceeded from the basin of the Mediterranean. The most essential share in its use seems to have belonged to the Moorish pilots, the Genoese, Venetians,