extremity. They are said to defend the nests, and stationing themselves near the outer surface, they are the first to make their appearance when their habitation is disturbed they will attack the party molesting them, and bite with considerable strength. The negroes and Hottentots consider these insects a great delicacy. They are destroyed with quick-lime, or more readily with arsenic, which is thrown into their habitations. The Psocidae are very small insects, having soft and swollen bodies: the head is very large, nearly trigonal, and provided with three ocelli on the upper surface.. The wings when folded meet at an angle above the abdomen, and are sparingly provided with nervures. The antennæ ure setaceous, and composed of about ten joints. The tarsi are short, and usually two-jointed. They are very active in their motions, and live in the bark of old trees and in dwelling-houses. Nearly forty species are said to be found in this country. TERMOLI. [SANNIO.] TERMONDE. [DENDERMONDE.] TERN, STERNA, the name of those web-footed long-winged birds which are vulgarly known as Sea-Swal lows. Linnæus, in his last edition of the Systema Naturæ, places the genus Sterna between Larus and Rhynchops. Cuvier arranges the Hirondelles de Mer between the Goelands (Larus) and Rhynchops. He observes that these Hirondelles de Mer derive their names from their excessively long and pointed wings, their forked tail, and their short legs, which give them a port and flight analogous to those of the Swallows. Their bill, he adds, is pointed, compressed, straight, without curvature or projection; their nostrils, situated towards the base, are oblong and pierced through; the membranes which unite their toes are very much notched, they therefore swim but little. They fly in all directions, and with rapidity over the sea, uttering loud cries and cleverly picking up from its surface the mollusks and small fishes which form their food. They also advance inland to lakes and rivers. Head and foot of Tern: The same author states that the Noddies may be distinguished from the other Sea-Swallows. Their tail is not forked. The views of Mr. Vigors, Mr. Swainson, and others, as to the position of the Terns, will be found in the article LARIDE. Mr. Swainson makes the genus Sterna consist of the following subgenera :-Sterna, Linn.; Thalassites, Sw. ; Phaeton, Linn.; Rhynchops, Linn.; Gavia, Briss. The Prince of Canino places Sternina, the second subfamily of his Larida, between the subfamilies Rhynchopsince and Larina. The Sternina consist of the following genera:- the Terns, which are widely diffused over the maritime parts of the globe, are noticed in the article LARIDE. The following have occurred, some occasionally only, in Europe : The Caspian Tern, Sterna Caspia (genus Stylochelidon, Brehm); The Sandwich Tern, Sterna Cantiaca (genus Thalasseus, Boie); the Gull-billed Tern, Sterna Anglica (genus Gelochelidon, Brehm); the common Tern, Sterna Hirundo (genus Sterna of authors); the Roseate Tern, Sterna Dougallii (genus Sterna); the Arctic Tern, Sterna Arctica (genus Sterna); the Little Tern, Sterna minuta (genus Sternula, Boie); the Noddy, Sterna stolida (genus Anous, Leach; Megalopterus, Boie); the Black Tern Sterna nigra (genus Hydrochelidon, Boie; Viralva Leach); the White-winged Tern, Sterna leucoptera (genus Hydrochelidon? Boie); and the Moustache Tern, Sterna leucopareia (genus Hydrochelidon? Boie; Viralva? Leach). Of these, the largest is the Caspian Tern. Our limits will not allow us to give more than two examples, and we select the Common Tern and the Noddy. We should premise that all the Terns of the British Islands are strictly migratory: many species visit us regularly for the purpose of breeding; but those, the Noddy for instance, whose home is far away, are seen casually and rarely. The Common Tern.-Description.-Forehead, top of the head, and long feathers of the occiput, deep black; posterior part of the neck, back, and wings, bluish ash; lower parts pure white, with the exception of the breast only, which is slightly clouded with ash-colour; quills whitish ash, terminated by ashy-brown; tail white, but the two lateral feathers blackish-brown on their external barbs; bill crimson-red, often blackish towards the point; iris reddish-brown; feet red. Length 13 to 14 inches. Such is M. Temminck's description of the adult male and female. The same author describes the young of the year before the autumnal moult as having the front, and a part of the top of the head, of a dirty white, marked towards the occiput with blackish patches; the long occipital feathers brownish-black; upper parts of tarnished bluish-ash; all these feathers bordered and terminated with whitish and irregularly spotted with brown or bright reddish; the lower parts of a dirty tarnished white; tail-feathers ashcoloured, terminated with whitish; base of the bill faded orange; iris blackish-brown; feet orange. This is the Pierre Garin of the French; Fionco and Rondine di Mare of the Italians; Meerschwalbe and Rothfussiger Meerschwalbe of the Germans; Zee-zwaluw of the Netherlanders; Kria of the Icelanders; Tende, Tendelobe, Sand-Tolle, and Sand-Tarrne of the Norwegians; Tærne of the Danes; Sea-Swallow of the modern British; and Y for-wennol fwyaf and Yscraean of the antient British. Geographical Distribution, Habits, &c.-The Common Tern,' says Mr. Gould, in his great work on the Birds of Europe, although not universally dispersed over our coasts, is nevertheless a very abundant species, being found in great numbers over the southern shores, but more sparingly over the northern, which are almost exclusively inhabited by its near ally, the Arctic Tern. It is now satisfactorily ascertained that the common Tern does not extend its range to the American continent, and that its place is there supplied by another species, to which the Prince of Musignano,' now Prince of Canino, has given the specific appellation of Wilsoni, in honour of the celebrated ornithologist by whom it was first described.' The Prince however gives both Sterna Wilsoni and Sterna Hirundo as American species, in his Birds of Europe and North America; and M. Temminck states that individuals killed in North America differ in nothing from those of Europe. In the fourth part of his Manuel (1840), though he adds to the synonyms and references, quoting among the rest Mr. Gould's work, he leaves his own observation above noticed uncontradicted. How far,' says Mr. Gould in continuation, the Common Tern is distributed over the Old Continent we have not satisfactorily ascertained, but we believe its range is extended from the Arctic Circle to the Mediterranean, and even to the coasts of Africa and India, to which southern and eastern countries it is supposed to retire during our winters. The Common Tern does not confine itself entirely to the sea, but frequently The Pelecanidae immediately follow. resorts to inland streams, &c.; and when thus ascending Geographical Distribution and Habits.-The habits of our creeks and rivers these little fairies of the ocean fear Sterna, Linn.; Hydrochelidon, Boie; Megalopterus, Boie (N.B. Sterna Stolida of authors); Thalasseus, Boie; Gelochelidon, Brehm; and Stylochelidon, Brehm. (Birds of Europe and North America.) Mr. G. R. Gray (Genera of Birds) arranges the Stermince as the third and last subfamily of Larida, immediately after Rhynchopinee, with the following genera :Phatusa, Wagl.; Gelochelidon, Brehm; Thalasseus, Boie; Stylochelidon, Brehm; Gygis, Wagl.; Sterna, Linn.; Sternula, Boie; Hydrochelidon, Boie; Anous, Leach (Sterna stolida, of authors); Onychoprion, Wagl.; and Pelecanopus, Wagl. P. C., No. 1517. VOL. XXIV.-2 H 2 S Π Mr. Nuttall gives a lively description of its habits. Familiar to mariners who navigate in the equatorial regions, the noddy, like the voyager, frequents the open seas to the distance of some hundreds of leagues from the land, and with many other birds of similar appetites and propensities, they are seen in great flights, assiduously following the shoals of their finny prey. They pursue them by flying near the surface of the water, and may now be seen continually dropping on the small fish, which ap proach the surface to shun the persecution of the greater kinds, by which they are also harassed. A rippling and silvery whiteness in the water marks the course of the timid and tumultuous shoals; and the whole air resounds with the clangor of these gluttonous and greedy birds, who, exulting or contending for success, fill the air with their varied but discordant cries. Where the strongest rippling appears, there the thickest swarm of noddies and sea-fowl are uniformly assembled. They frequently fly on board of ships at sea, and are so stupid or indolent on such occasions, as to suffer themselves to be taken by the hand from the yards on which they settle: they sometimes however, when seized, bite and scratch with great resolu tion, leading one to imagine that they are disabled often from flight by excessive fatigue or hunger. Some have imagined that the appearance of the noddy at sea indicates the proximity of land; but in the manner of the common tern, they adventure out to sea, and, like the mariner himself, the shelter of whose friendly vessel they seek, they often voyage at random for several days at a time, committing themselves to the mercy of the boundless ocean; and having at certain seasons no predilection for places, where the climate suits, the roving flocks or stragglers find equally a home on every coast, shoal, or island.' (Manual of Ornithology.) The vessel however is not always friendly. Bligh found the bird a seasonable supply to himself and his famished crew in his celebrated boat-voyage after the mutiny of the Bounty [BLIGH]; and Byron has improved the incident in the terrible scene after the shipwreck in Don Juan.' [BOOBY, vol. v., p. 159.] TERNATE, an island in the Indian Archipelago, is traversed by 50' N. lat. and 127° 20' E. long. It is 10 miles long and from four to five miles wide. It derives its reputation from the circumstance that its sovereign is in possession of a considerable portion of the islands of Gilolo and Celebes; and on this account the Dutch have thought it expedient to form a considerable establishment on the island at Fort Orange. The northern group of the Moluccas has been called the Ternate Islands, though this island is only one of the smaller ones which belong to them, some of which are of great extent, especially Gilolo. The greater part of the island appears to be occupied by a volcano, which, according to Valentyn, attains an elevation of 367 ruths and 2 feet, or 4095 feet English, above the sea-level. The remainder of the island is very fertile, and affords rice and the other productions of the Indian Archipelago: but we have very little information on these points, as the Dutch have always excluded foreigners, and prevent the natives from trading with the neighbouring islands, lest the spices which grow on this and other islands of the group should be brought to other countries by any other channel than their own commerce; and although the English have been twice in possession of the Dutch settlement, their attention has been more directed to the great Dutch colonies than to this comparatively small establishment. We learn only from Forrest, that the inhabitants of the Sooloo Archipelago were permitted to trade with Ternate, and that they imported large quantities of different articles of Chinese manufacture, which they exchanged for rice, edible birds'nests, trepang, sharks' fins, tortoise-shells, and small pearls: they exported also a great number of lories. The inhabitants are Malays, who have embraced Islam. There are three mosques. The king, who possesses also the northern part of Gilolo, and the north-eastern limb of Celebes, where the Dutch have two settlements at Manado and Gurontalu, and several of the adjacent islands, lives in great state. These countries however are governed by separate chiefs, who in many respects resemble the feudal aristocracy of the middle ages: but the king and the chiefs are dependent on the Dutch governor of Amboyna, of which government Ternate forms a regency. Ternate was first visited by the Portuguese in 1521, and some years afterwards they formed a settlement, which passed into the hands of the Dutch in 1606; who, in 1680, reduced the king to a state of dependence on them, and enlarged their establishment. In 1797 it was taken, together with Amboyna, by the English, who restored it at the peace in 1801: it was again taken in 1810, and again given up to Holland by the treaty of Paris in 1814. (Forrest's Voyage to New Guinea and the Moluccas, c. Stavorinus's Voyages to the East Indies; Von Buch's Physikalische Beschreibung der Canarischen Inseln, fc.) TERNI. [SPOLETO.] TERNSTRÖMIA'CEÆ, a natural order of plants belonging to the Calycose group of polypetalous Dicotyledons. As at present constituted, by Cambessedes, who is followed by Lindley, this order consists of trees or shrubs with alternate coriaceous leaves, without stipules, mostly undivided, and sometimes with pellucid dots. The flowers are generally white in colour, sometimes pink or red, and are arranged in axillary or terminal peduncles, articulated at the base. The calyx is composed of 5 or 7 sepals, imbricated in æstivation, the innermost the largest; petals 5, 6, or 9, often combined at the base; stamens indefinite with monadelphous or polyadelphous filaments, and versatile or adnate anthers; ovary superior; capsule 27 celled; seeds few, attached to a central axis, with little or no albumen, and a straight embryo, the cotyledons of which are very large, and often filled with oil. This order includes the Theaceae of Mirbel and the Camelliea of De Candolle. Their closest affinity is with the order Guttiferæ, from which they differ in their alternate leaves; in the parts of their flowers being 5 and its multiples; in the calyx being distinct from the corolla; in their twisted æstivation, and in their thin inadherent cotyledons. They have also relations with Hypericacea and Marcgraaviacæ. The plants of this order are principally inhabitants of Asia and America; one species only is a native of Africa. This order includes the genus Thea, and hence is one of great economical importance. [THEA.] It is supposed that the dried leaves brought to this country under the name of tea are not alone the produce of the genus Thea, but that the leaves of some species of Camellia are also mixed with them. [CAMELLIA. Independent of these two genera, little is known of the properties of this order. The Cochlospermum insigne is used as a medicine in internal bruises in Brazil, where it is called Butua do curvo. The C. tinctorium yields a yellow dye; and the seeds of C. Gossypium yield a gum resembling Tragacanth, for which it is substituted. 1, branch with flowers and leaves; 2, superior ovary with trifid stigna; 3, fruit entire; 4, capsule dehiscent. TERPA'NDER (Tpravopos), the earliest and the most important historical personage in the history of Greek music and its connection with poetry, for he was both a musician and a poet. He was a native of Antissa, in the island of Lesbos, and his best period falls in the latter half of the seventh century before Christ. There are few events in his life that can be chronologically established. In B.C. 676, at the first celebration of the musical contests during the festival of the Carneia near Sparta, Terpander was crowned as victor. (Athenæus, xiv., p. 635.) He afterwards gained four successive prizes in the musical contests at the Pythian games (Plutarch, De Musica, 4); and these victories probably fall between the years 672 and 645 B.C., since in the latter of these years he was at Sparta, and there introduced his nomes (vóuot) for singing to the accompaniment of the cithara, and was engaged in reducing the music of the Greeks, such as it then was, to a regular system. (Marmor. Parium, Epoch. 34; Plutarch, De Mus., 9.) At this time his fame must have reached its height. His descendants, or at least the musicians of his school (Kapwdoi), continued for more than a century to obtain the prize at the Carneia every year without any interruption. Numerous musical inventions are said to have been made by Terpander; many of them however may have been made by other persons, especially such as belonged to his school, and were subsequently ascribed to the father and founder of the art. Of many of his inventions we are unable to form any clear idea. The most important among them however is the seven-stringed cithara (heptachord). Previous to his time songs, hymns, and rhapsodies had been accompanied with a cithara of only four strings (tetrachord), to which Terpander added three new strings, so as to make the cithara comprise a full octave, or, as the Greeks called it, a diapason. The heptachord soon came into general use, and remained the favourite instrument of the Greeks, especially the Dorians, notwithstanding the various alterations and improvements that were made. Another very important improvement which the antients unanimously assign to Terpander, is the reduction of the antient melodies to certain systems (vópot), which continued unaltered for several centuries. These nomes appear to have been of a twofold character: he either invented them himself, or he merely fixed those which had been used before his time. This fixing of certain tunes and melodies he is said to have effected by marks or notes which he made over the verses of a poem. In this manner he marked the tunes of his own poems, as well as of portions of the Homeric rhapsodies. His own poetical compositions, which, with the exceptions of a few fragments, are now lost, consisted of hymns, procenia, and scolia. (Müller, History of the Literature of Antient Greece, 1., p. 149, &c.; Bode, Geschichte der Lyrische Dichtkunst der Hellenen, ii., p. 363, &c.) TERPSICHORE. [MUSES.] TERRA DI LAVORO. [LAVORO, TERRA DI.] TERRACI'NA, a town of the Papal State, in the administrative province of Frosinone, near the borders of the kingdom of Naples, and on the high road from Rome to Naples. The old town, which is built on the site of the antient Anxur, rises in the form of an amphitheatre on the slope of a calcareous rock which is a projection of the ridge called | Monti Lepini, leaving but a narrow strip of land between it and the sea, along which runs the high road to Naples in the track of the antient Via Appia. Along the road are the modern buildings of Terracina, constructed by Pius VI., and consisting of the post-house and inns, customhouse, granaries, and other structures for public use. The old harbour, which was restored by the emperor Antoninus, has been long since filled up, but remains of the mole are still seen. The old town is an assemblage of poor-looking houses, perched one above another, surrounded and overtopped by white cliffs which are seen from afar (Horace, Sat. i. 5), and intermixed with myrtle, orange, and palm trees, and with plants of aloes and cactus. Above all rise the cathedral with its lofty steeple, an elegant palace built by Pius VI., the remains of the palace called that of Theodoric, which is a structure of the fifth century of our æra, and is situated on the summit of the hill, and about 600 feet above the sea, and an old castle raised in the middle ages. The cathedral is ornamented with some fine fluted Corinthian columns, which have been taken from a temple of Jupiter now ruined. Remains of a theatre are also seen. The climate of Terracina is very mild and genial in winter, but is unwholesome in summer. The population of the town is 4000 inhabitants. Terracina is 56 miles south-east of Rome and 59 miles northwest of Naples. Beyond Terracina, on the side towards Naples, is a detached rock of a pyramidical form, nearly 200 feet high, one side of which was cut perpendicularly by C. Appius to make room for his road. About two miles farther is the frontier of Rome and Naples, where a military post is kept by each respective state. (Tournon, Etudes Statistiques sur Rome; Valéry, Voyages en Italie; Calindri, Saggio Statistico dello Stato Pontificio.) Anxur was a thriving town of the Volsci long before the Roman conquest, was taken by the Romans in the year 403 B.C., was retaken by surprise in 399, and taken again by the Romans three years after. It afterwards became a Roman colony by the name of Tarracina. During the second Punic war the temple of Jupiter at Tarracina is mentioned by Livy as having been struck by lightning. (Livy, iv. 59; v. 10-13; xxviii. 11.) TERRANOVA. [SICILY.] TERRAPE'NE. [TORTOISES.] TERRASSON, JEAN, a French writer of the last century. He was born at Lyon, A.D. 1670: his father was the Congregation, but Jean (now a sub-deacon) whose disposition disinclined him to the life of an ecclesiastic, quitted the Society, not however without having acquired considerable acquaintance with theology. The simplicity of character which ever distinguished him rendered him the dupe of men, by whom his small patrimony was soon wasted; but he found a shelter in the house of a friend, M. Rémond, to whose son he became tutor. He subsequently (A.D. 1714) undertook the education of the son of his cousin Mathieu Terrasson, a celebrated advocate in the parliament of Paris. He had become an associate of the Académie Royale des Sciences, A.D. 1707. In 1715 he made his first appearance as an author by taking part in the dispute then raging on the value of the Homeric Poems, and the comparative merits of the antients and moderns. His work was entitled Dissertation Critique sur Iliade d'Homère,' 2 vols. 12mo., Paris: it met with a favourable reception from those who joined in or approved of the attacks then made on Homer, who was severely criticized. Next year Terrasson published an addition to his dissertation on Homer, in 12mo., in reply to André Dacier, by whom he had been attacked. In A.D. 1719 the financial system of Law enabled Terrasson to obtain a large fortune, and induced him to form an establishment and set up his carriage: but wealth was to him rather a source of embarrassment than of pleasure; and when he lost his fortune the next year in the financial change which took place, he contentedly observed that it would be more convenient to him to live on a little. In A.D. 1720 he published a small work in defence of Law's financial schemes, entitled Trois Lettres sur le Nouveau Système des Finances,' 56 pp., 4to., Paris, and another small work in defence of the French India Company. He saved some small part of his fortune from the general wreck; and this, with the income of a professorship, which he obtained next year (A.D. 1721) in the Collège Royal, and a pension subsequently conferred by the crown, rendered his circumstances easy for the rest of his life. He became a member of the Académie Française A.D. 1732. In 1731 Terrasson published a romance in imitation of the Telemaque' of Fénélon. It was entitled Sethe 3 vols. 12mo., Paris, and professed to be a translation of a Greek manuscript. The scene is laid chiefly in Egypt. This work obtained sufficient circulation to go through several editions, of which the last was in 1813, in 6 vols. 18mo., but never became popular. An English transla tion was published in London in 1732. In the years 1737-44 he published the seven successive volumes in 12mo. of a translation of Diodorus Siculus. This transla tion has been reprinted once or twice, but is very inaccurate. This was his last work of any extent. His memory and his bodily strength gradually failed, and he died A.D. 1750, aged 80. He wrote also a treatise entitled De l'Infini Créé,' of which he allowed one or two transcripts to be taken during his life; but it was never published, nor was the original manuscript found among his papers at his decease. He left also a small work, published after his decease, entitled La Philosophie applicable à tous les Objets de l'Esprit et de la Raison' (Paris, 8vo., 1754). From an anonymous letter printed, with one or two other pieces, at the commencement of this small volume, and containing a biographical notice of Terrasson, we have derived the substance of this article. See also the Eloge de Terrasson, by D'Alembert; Quérard, La France Littéraire; Biographie Universelle. TERRESTRIAL MAGNETISM. This term is used to denote the action of the magnetic fluid in or about the earth; the effects of that action being manifested in the phenomena presented by magnetized needles or bars. The general polarity of a magnetized needle when supported or suspended in a balanced state, and its inclination to the horizon, with the slow variations to which those elements, as well as the intensity of the magnetic force, are subject, are phenomena which are conceived to arise from causes existing in the earth and pervading its whole mass; Pierre Terrasson, one of a family of considerable eminence the needle, are supposed to depend upon electrical cure while the temporary effects, as the diurnal variations of and activity in that city, and a man whose devout temper rents produced by variations of temperature at the surface led him to make all his four sons (of whom Jean was the in consequence of the changes in the sun's position with eldest) members of the Congregation of the Oratory. respect to the horizon, and perhaps from other circumtheir father died: the three younger remained members of in the upper regions of the atmosphere may be the causes electricity of those occasional agitations in the needle, to which the name of magnetic storms has been lately applied, and which are now known to extend at the same moment over a great portion of the earth's surface. The declination (variation) of the needle is that element of terrestrial magnetism which was first observed, and the difference of its amount in different regions, as well as the annual change at the same station, was early noticed. Dr. Halley, on his return to England after his second voyage, during which he had made many observations on the variation in different parts of the Atlantic and Pacific oceans, published, in 1701, a chart, on which were traced what have been since called isogonal lines, that is, lines passing through the points on the earth's surface where the variation was the same; and other charts of a like kind have since at different times been constructed. The expectation at first entertained, that such a chart might serve as a means of ascertaining the longitude of a ship at sea by an observed variation of the needle has not however been fulfilled, since as yet no formula has been discovered by which the variation at any given time and place may with sufficient accuracy be found: but though the changes of the variation have hitherto rendered such charts of little use for the purposes of navigation, yet a knowledge of the form of the lines of equal variation at different periods may be of great importance as a step to the discovery of the law of those changes. The latest variation chart is one which was published by Adolf Erman, after his journey, in company with Hansteen and Due, through the whole length of the Russian empire, and his return to Europe by sea. Erman determined the positions of the isogonal lines from his own observations, and from the most authentic of those which had been made by other observers between the years 1827 and 1830; and subjoined is a representation of the principal lines on the two hemispheres of the earth, projected stereographically on the plane of the equator. The lines marked oo pass through places where the variation is zero; the positive sign before a number indicates that the variation is westward, or that the needle deviates to the west of the astronomical meridian; and the negative sign indicates that the variation is eastward. On an inspection of the lines, it is manifest that on a sphere they must be curves of double curvature with bends in opposite directions; that most of them converge towards two points on the earth's surface, one in or near Baffin's Bay, and the other to the southward of New Holland; and that between the inflexions there are some which return into themselves. The dip, or inclination of the needle to the horizon, | mum, may be fixed at a point (P in the diagram) in which is another element of terrestrial magnetism, was first recorded by Robert Norman [INCLINATION], and numerous observations have been made to ascertain its value in different parts of the world, together with the variations to which it is subject in process of time; but a general chart exhibiting the forms of the isoclinal lines, as those of equal dip are called, is still wanting. On the above cut are represented by dotted curves some of the lines which are best known; and these have been taken chiefly from the partial chart given by Major (now Colonel) Sabine, in the Philosophical Transactions' for 1840. The data are stated to have been obtained from above 140 observations made on land between 1834 and 1839, and from many which were made at sea by Mr. Dunlop in 1831, and by Lieut. Sulivan in 1839. Some points have also been taken from the observations made by Erman in the Pacific Ocean, of which last observations a table is given in the 'Seventh Report of the British Association' (vol. vi.). long. 263° (117° west), and in lat. 70° N.: at that place, by the observations of Captain James Ross, the dip in 1831 was found to be 89° 59'. Professor Hansteen, of Christiania, has deduced, from the observations which have been made in the polar regions, that the isogonal lines in the northern hemisphere tend to two points in the vicinity of the pole of the dip; those which are on the north side uniting in a point a little way to the north of the latter pole, and those on the south side a little way to the south of the same pole. a, a, a, represents the line of no dip, which is evidently a curve of double curvature, and crosses the terrestrial equator in two points at least: b, b, b, is the known portion of the isoclinal line for a dip of 30 degrees below the northern part of the horizon: c, c, is the line for 60°; and d, d, the line for 75°. An inspection of the cut will show that the oval lines of equal dip go on diminishing in magnitude northwards, and the pole of the dip, or place where that element is a maxi Till within the last fifty years it was the general opinion that the intensity of terrestrial magnetism was the same at all parts of the earth's surface; and to the Académie des Sciences, in France, is due the honour of having been the first learned body which proposed that observations should be made for the purpose of determining that element. In the instructions which its members drew up for the use of the unfortunate La Perouse, it was recommended that the intensity should be observed at places very distant from one another, in order to ascertain whether or not any differences existed in its value. The accounts of any observations which may have been made during the voyage perished; but between the years 1791 and 1794, M. Rossel, who sailed from France with the expedition in search of La Perouse, determined with a dipping-needle the inclination to the horizon, and the times of performing a vibration, at different places; and from the latter the fact of a difference |