# Encyclopædia Britannica, Ninth Edition/Compass, Mariner's

See also Mariner's compass on Wikipedia; Compass in the 11th Edition; and the disclaimer.
COMPASS, The Mariner's, consists of three principal parts,—the card, the needle on its lower surface, and the case. The whole is enclosed in the compass-box, or binnacle. The term compass is said to have been applied to the instrument because the card involves or the compasses whole plane of the horizon, or because the needle indicates the whole circle of possible variations of direction. The surface of the card is divided by radiating lines into 32 parts, each containing 11° 15ʹ; these constitute the 32 points or rhumbs; the half-points and quarters are subdivisions of the same. The north pole is denoted on the card a by fleur-de-lis; and the line which joins the north and south poles passes through the axis of the needle. The points are named according to their to the four cardinal proximity points; for instance, the point mid-way between N. and N.E. is called north-north-east, being nearer north than east, and is marked N.N.E; the point mid-way between N. and N.N.E. is termed north by east, and is marked N. by E. The circumference of the card is sometimes divided into 360°. The divisions of the card are shown in the accompanying figure. The card is directed by the needle,
which, with it, is pivoted on a vertical axis. With a little variation, the needle points nearly to the geographical north, and hence the mode of steering by the compass. Four or more parallel magnets, with like poles pointing in like directions, may be combined to form the needle; and by this arrangement the magnetic moment is increased for a given weight of steel. The needle is usually suspended on a central cap of ruby or agate, the point of suspension being of a similar hard material. On the inside of the compass-box is a vertical line known as lubber’s point; and since this and the pivot of the card are in the same plane with the ship’s keel, the point on the circumference of the card opposite to lubber’s point shows the angle the ship’s course makes with the magnetic meridian. The compass is kept horizontal by the use of a gimbal, or ring moving freely on an axis, within which it swings on an axis at right angles. In the azimuth compass the circumference of the card is divided into degrees and parts by a vernier, and is fitted up with sight-vanes to take amplitudes and azimuths, for the purpose of determining the variation of the compass by observation. The variation is applied to the magnetic course shown by the steering compass, and thus the true course with respect to the meridian becomes known.
{{ti|1em|The earliest references to the use of the compass are to be found in Chinese history, from which we learn how, in the sixty-fourth year of the reign of Ho-ang-ti (2634 b.c.), the emperor Hiuan-yuan, or Ho-ang-ti, attacked one Tchi-yeou, on the plains of Tchou-lou, and finding his army embarrassed by a thick fog raised by the enemy, constructed a chariot (Tchi-nan) for indicating the south, so as to distinguish the four cardinal points, and was thus enabled to pursue Tchi-yeou, and take him prisoner. (Klaproth, Lettre à M. le Baron Humboldt sur l’invention de la Boussole, Paris, 1834. See also Mailla, Histoire générale de la Chine, tom. i. p. 316, Paris, 1777.) Several other allusions to the compass are contained in early Chinese records. The power of the loadstone to communicate polarity to iron is said to be for the first time explicitly mentioned in a Chinese dictionary, finished in 121 a.d., where the loadstone is defined as “a stone with which an attraction can be given to the needle.” The first mention of the use of the compass for the purpose of navigation—an art that has apparently retrograded rather than advanced among the Chinese—occurs in the Chinese encyclopædia, Poci-wen-yun-fou, in which it is stated that under the Tsin dynasty, or between 265 and 419 a.d., “there were ships directed to the south by the needle.” The Chinese, Mr Davis informs us, once navigated as far as India, but their most distant voyages at present extend not further than Java and the Malay Islands to the south (The Chinese, vol. iii. p. 14, London, 1844). According to an Arabic manuscript, a translation of which was published by Eusebius Renaudot (Paris, 1718), they traded in ships to the Persian Gulf and Red Sea in the 9th century. Staunton, in vol. i. of his Embassy to China (London, 1797), after referring to the early acquaintance of the Chinese with the property of the magnet to point southwards, remarks (p. 445), “The nature and the cause of the qualities of the magnet have at all times been subjects of contemplation among the Chinese. The Chinese name for the compass is ting-nan-ching, or needle pointing to the south; and a distinguishing mark is fixed on the magnet’s southern pole, as in European compasses upon the northern one.” “The sphere of Chinese navigation,” he tells us (p. 447), “is too limited to have afforded experience and observation for forming any system of laws supposed to govern the variation of the needle…The Chinese had soon occasion to perceive how much more essential the perfection of the compass was to the superior navigators of Europe than to themselves, as the commanders of the ‘Lion’ and ‘Hindostan,’ trusting to that instrument, stood out directly from the land into the sea.” The number of points of the compass, according to the Chinese, is twenty-four, which are reckoned from the south pole; the form also of the instrument they employ is different from that familiar to Europeans. The needle is peculiarly poised, with its point of suspension a little below its centre of gravity, and is exceedingly sensitive; it is seldom more than an inch in length, and is less than a line in thickness. It appears thus sufficiently evident that the Chinese are not indebted to Western nations for their knowledge of the use of the compass. “It may be urged,” writes Mr T. S. Davies, “that the different manner of constructing the needle amongst the Chinese and European navigators shows the independence of the Chinese of us, as theirs is the worse method, and had they copied from us, they would have used the better one (Thomson’s British Annual, 1837, p. 291). On the other hand, it does not seem improbable that a knowledge of the mariner’s compass was communicated by them directly or indirectly to the early Arabs, and through the latter was introduced into Europe. Sismondi has remarked (Literature of Europe, vol i.) that it is peculiarly characteristic of all the pretended discoveries of the Middle Ages that when the historians mention them for the first time they treat them as things in general use. Gunpowder, the compass, the Arabic numerals, and paper, are nowhere spoken of as discoveries, and yet they must have wrought a total change in war, in navigation, in science, and in education. Tiraboschi (Storia della Letteratura Italiana, tom. iv. lib. ii. p. 204, et seq., ed. 2., 1788), in support of the conjecture that the compass was introduced into Europe by the Arabs, adduces their superiority in scientific learning, and their early skill in navigation. He quotes a passage on the polarity of the loadstone from a treatise translated by Albertus Magnus, attributed by the latter to Aristotle, but apparently only an Arabic compilation from the works of various philosophers. As the terms Zoron and Aphron, used there to signify the south and north poles, are neither Latin nor Greek, Tiraboschi suggests that they may be of Arabian origin, and that the whole passage concerning the loadstone may have been added to the original treatise by the Arabian translators.
{{ti|1em|Again, it appears that compasses of a primitive description, which can hardly be supposed to have been brought from Europe, were employed in the East Indies certainly as early as several years previous to the close of the 16th century In William Marlowe s Navigator s Supply, published in 1597, we read: " Some fewe yeeres since, it so fell out that I had several! conferences with two East Indians which were brought into England by master Candisu [Thomas Cavendish], and had learned our language : The one of them was of Mamillia [Manilla] in the Isle of Luzon, the other of Miaco in Japan. I questioned with them concerning their shipping and manner of sayling. They described all things farre different from ours, and shewed, that in steade of our Compas, they use a magneticall needle of sixe ynches long, and longer, upon a pinne in a dish of white China earth filled with water ; In the bottome whereof they have two crosse lines, for the foure principall windes; the rest of the divisions being reserved to the skill of their Pilots. " Bailak Kibdjaki, also, an Arabian writer, shows in his Merchant's Treasure, a work given to the world in 1282, that the magnetized needle, floated on water by means of a splinter of wood or a reed, was employed on the Syrian seas at the time of his voyage from Tripoli to Alexandria (1242), and adds : "They say that the captains who navigate the Indian seas use, instead of the needle and splinter, a sort of fish made out of hollow iron, which, when thrown into the water, swims upon the surface, and points out the north and south with its head and tail " (Klaproth, Lettrc, p. 57). Furthermore, although the sailors in the Indian vessels in which Niccola de Conti traversed the Indian seas in 1420 are stated to have had no compass, still, on board the ship in which Varthema, less than a century later, sailed from Borneo to Java, both the mariner's chart and compass were used; it has been questioned, however, whether in this case the compass was of Eastern manufacture (Travels of Varthema, Introd. xciv., and p. 249). We have already seen that the Chinese as -late as the end of the 18th century made
The Saracen geographer, Edrisi, who lived about 1100, is said by Boucher to give an account, though in a confused manner, of the polarity of the magnet (Hallam, Mid. Ages, vol. iii. chap. 9, part 2) ; but the earliest definite mention as yet known of the use of the mariner s compass in the Middle Ages occurs in a treatise entitled DC Utensilibus, written by Alexander Neckam in the 12th century. He speaks there of a needle carried on board ship which, being placed on a pivot, and allowed to take its own position of repose, shows mariners their course when the polar star is hidden. In another work, De Naturis Rcrum, lib. ii. c. 89, he writes, "Mariners at sea, when, through cloudy weather in the day which hides the sun, or through the darkness of the night, they lose the knowledge of the quarter of the world to which they are sailing, touch a needle with the magnet, which will turn round till, on its motion ceasing, its point will be directed towards the north 11 (W. Chappell, Nature, No. 346, June 15, 1876). The magnetical needle, and its suspension on a stick or straw in water, are clearly described in La Bible Guiot, a poem probably of the 13th century, by Guiot de Provins, wherein we are told that through the magnet (la manette or I amaniere), an ugly brown stone to which iron turns of its own accord, mariners possess an art that cannot fail them. A needle touched by it, and floated by a stick on water, turns its point towards the pole-star, and a light being placed near the needle on dark nights, the proper course is known (Hist, litttraire de la France, torn. ix. p. 199 ; Barbazan, Fabliaux, torn. ii. p. 328). Cardinal Jacques do Vitry, bishop of Aeon in Palestine, in his History (cap. 89), written about the year 1218, speaks of the magnetic needle as w most necessary for such as sail the sea ; ' and another French crusader, his contemporary, Vincent de Beauvais, states that the adamant (loadstone) is found in Arabia, and mentions a method of using a needle magnetized by it which is similar to that described by Kibdjaki. From quotations given by Antonio Capmany (Questiones Crilicas) from the De Contemplations of Raymond Lully, of the date 1272, it appears that the latter was well acquainted with the use of the magnet at sea ; and before the middle of the 13th century Gauthier d Espinois alludes to its polarity, as if generally known, in the lines : —
"Tons autresi cojnme 1 ainiant deceit [detournej
L aiguillette par force de vertu,
A ma dame tot lc mont [monde] retcnuo Qui sa beaute" council et apercoit."
Guklo Guinizzelli, a poet of the same period, writes : "In those parts under the north are the mountains of loadstone, which give the virtue to the air of attracting iron ; but because it [the load stone] is far off, [it] wishes to have the help of a similar stone to make it [the virtue] work, and to direct the needle towards the star. Brunetto Latini also makes reference to the compass in his encyclopaedia Livres dou tresor, composed about 1 260 ; and a letter written in 1269, attribiited to Peter Adsiger, shows that the declination of the needle had already been observed at that date. From Torfajus we learn that the compass, fitted into a box, was already in use among the Norwegians about the middle of the 13th century (Hist, Rcr. Norvcgicarum, iv. c. 4, p. 345, Hafnia?, 1711) ; and it is probable that the use of the magnet at sea was known in Scotland at or shortly subsequent to that time, though King Robert, in crossing from Arran to Carrick in 1306, as Harbour writing in 1375 informs us, "na nedill had na stane," but steered by a fire on the shore.
From the above it will have been evident that, as Barlowe remarks concerning the compass, " the lame tale of one Flavius at Amelphus, in the kmgdome of Naples [Flavio Gioja of Amalp-hi, cir 1307], for to have devised it, is of very slender probabilitie ; " and as regards the assertion of Dr Gilbert, of Colchester (De Magnete, p. 4, 1600), that Marco Polo introduced the compass into Italy from the East in 1260, we need only quote the words of Col. Yule (Book of Marco Polo) : " Respecting the mariner s compass and gunpowder, 1 shall say nothing, as no one now, I believe, imagines Marco to have had anything to do with their introduction."
When and by whom the card was added are still matters of conjecture ; but the thirty-two points or rhumbs into which it is divided were recognized at least as early as the time of Chaucer, who, in 1391, wrote, "Now is thin Orisonte departed in xxiiii partiez by thi azymutz, in significacion of xxiiii partiez of the world ; al be it so that ship men rikne thilke partiez in xxxii " ( Treatise on the Astrolabe, ed. Skeat, Early Eng. Text Soc., Lond. 1872).
"Out of Bristowe and costes many one, Men haue practised by nedle and by stone Thider wardes within alitle while." Hakluyt, Principal Navigations, p. 201, Lond. 1599.
From this it would seem that the compasses used at that time by English mariners were of a very primitive description. Barlowe, in his treatise Magnetical Advertisements, printed in 1616 (p. 66), complains that "the Compasse needle, being the most admirable and usefull instrument of the whole world, is both amongst ours and other nations for the most part, so bungerly and absurdly contrived, as nothing more." The form he recommends for the needle is that of "a true circle, having his Axis going out beyond the circle, at each end narrow and narrower, unto a reasonable sharpe point, and being pure steele as the circle it selfe is, having in the middest a convenient receptacle to place the capitell in." In 1750 Dr Gowan Knight found that the needles of merchant-ships were made of two pieces of steel bent in the middle and united in the shape of a rhombus, and proposed to substitute straight steel bars of small breadth, suspended edgewise, and hardened throughout. He also showed that the Chinese mode of suspending the needle conduces most to sensibility. In 1820 Prof. Barlow reported to the Admiralty that half the compasses in the Royal Navy were mere lumber, and ought to be destroyed. Since then many improved varieties of ships compasses have been introduced, of which may be mentioned those of Pope, Preston, Walker, Dent, Stebbing, Gowland, Gray, Duchemin, and Harris. In the last the needle turns upon a point which is the centre of a doubly-curved bar of copper, fixed as a diameter to a ring of the same metal. In the Admiralty compass the bowl is of copper, the card of mica; and compound magnetic bars, as proposed by Scoresby, are employed.}}
B, Corrector for quadrantal error; C, Box for corrector; a, Aluminium boss; b. Central cap of sapphire; c, Cords connecting rim and boss; d, Magnets e, Threads connecting magnets; f, Aluminium rim; f′, Cords supporting magnets; g.g′. Knife edges for gimbals.
The most remarkable and, as shown by trial, most satisfactory form of the compass is that patented in 1876 by Sir William Thomson (see fig. 2). The card consists of a central boss and an outer rim, both of aluminium, connected together by fine silk cords. Eight or twelve small magnets, 2 to 3 inches long, having their corresponding ends tied together by threads of equal lengths, are suspended by silk cords from the rim, to which is attached thin paper marked with the points of the compass and degrees. The concentration, in this wise, of the greater part of the weight in the rim gives a long period of free oscillation, and consequently great steadiness; and as the card of a 10-inch compass, with its suspended needle and sapphire, weighs only 178 grains, the frictional error is very slight. Owing to the smallness of the needles, a perfect correction for all latitudes of a quadrantal error of 5 or 6 degrees for a 10-inch, and of 11 or 12 degrees for a 7-inch compass can be effected by means of a couple of iron globes not more than 6 inches in diameter, fixed on opposite sides of the binnacle. The thwart-ship and the fore-and-aft components of the ship's magnetic force are neutralized by two adjustable correctors placed one over the other, and so arranged that in their zero position the middle line of both is vertically under the centre of the compass. Each corrector consists of two bar magnets movable round a common horizontal axis perpendicular to their lengths. To correct the heeling error, an adjustable magnet is applied below the compass in a line through its centre perpendicular to the deck. For taking bearings, a new instrument, the azimuth mirror, is provided, whereby the image of the object reflected from a plane mirror is thrown, as in a camera lucida, on the graduated circle of the compass card, and is seen through a convex lens. Another improvement is the use of knife edges instead of journals for supporting the gimbals. A hemispherical space below the compass-case, nearly filled with castor-oil, serves to calm the vibrations of the bowl.
See articles Magnetism and Navigation; Cavallo, Treatise on Magnetism, 2d ed., Lond. 1800; Macpherson, Annals of Commerce, 1805; Airy, Phil. Trans., 1839, and 1846, part i., and Magnetism, sect, x., 1870; Johnson, On the Deviations of the Compass, 1852; Evans, Phil. Trans., 1860; Scoresby, The Compass in Iron Ships, 1855, &c.; Evans and Smith, The Admiralty Manual of the Compass; Merrifield, Magnetism and the Deviation of the Compass, part ii., 1872; Harris, Rud. Treat. on Magnetism, 1872; Thomson, in Nature, vol. x. p. 388, 1874.
(f. h. b.)
* ↑ According to Mr T. S. Davies, this may originally have been an ornamented cross.
* ↑ Adamas in India reperitur .....Ferrum occulta quadam natura ad se trahit. Acus ferrea postquam adamantem contigerit, ad stellam septentrionalem ..... semper convertitur, unde valde uecessarius est navigantibus in mari.
* ↑ Sicut acus per naturam vertitur ad septentrionem dum sit tacta a magnete.— Sicut acus nautica dirigit marinarios in sua navigutione.
* ↑ Ginguene, Hist. lit. de I Italic, t. i. p. 413.
* ↑ "According to all the texts he returned to Venice in 1295 or, as is more probable, in 1296."—Yule.