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Thursday, November 21st, 2024
the Week of Proper 28 / Ordinary 33
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Compass
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(Fr. compas, ultimately from Lat. cum, with, and passus, step), a term of which the evolution of the various meanings is obscure; the general sense is "measure" or "measurement," and the word is used thus in various derived meanings - area, boundary, circuit. It is also more particularly applied to a mathematical instrument ("pair of compasses") for measuring or for describing a circle, and to the mariner's compass.
The mariner's compass, with which this article is concerned, is an instrument by means of which the directive force of that great magnet, the Earth, upon a freely-suspended needle, is utilized for a purpose essential to navigation. The needle is so mounted that it only moves freely in the horizontal plane, and therefore the horizontal component of the earth's force alone directs it. The direction assumed by the needle is not generally towards the geographical north, but diverges towards the east or west of it, making a horizontal angle with the true FIG. I. - Compass Card.
meridian, called the magnetic variation or declination; amongst mariners this angle is known as the variation of the compass. In the usual navigable waters of the world the variation alters from 30° to the east to 45° to the west of the geographical meridian, being westerly in the Atlantic and Indian oceans, easterly in the Pacific. The vertical plane passing through the longitudinal axis of such a needle is known as the magnetic meridian. Following the first chart of lines of equal variation compiled by Edmund Halley in 1700, charts of similar type have been published from time to time embodying recent observations and corrected for the secular change, thus providing seamen with values of the variation accurate to about 30' of arc. Possessing these data, it is easy to ascertain by observation the effects of the iron in a ship in disturbing the compass, and it will be found for the most part in every vessel that the needle is deflected from the magnetic meridian by a horizontal angle called the deviation of the compass; in some directions of the ship's head adding to the known variation of the place, in other directions subtracting from it. Local magnetic disturbance of the needle due to magnetic rocks is observed on land in all parts of the world, and in certain places extends to the land under the sea, affecting the compasses on board the ships passing over it. The general direction of these disturbances in the northern hemisphere is an attraction of the north-seeking end of the needle; in the southern hemisphere, its repulsion. The approaches to Cossack, North Australia; Cape St Francis, Labrador; the coasts of Madagascar and Iceland, are remarkable for such disturbance of the compass.
The compass as we know it is the result of the necessities of navigation, which have increased from century to century. It consists of five principal parts - the card, the needles, the bowl, a jewelled cap and the pivot. The card or "fly," formerly made of cardboard, now consists of a disk either of mica covered with paper or of paper alone, but in all cases the card is divided into points and degrees as shown in fig. 1. The outer margin is divided into degrees with o° at north and south, and 90° at east F F FIG. 2. - Admiralty Compass FIG. 3. - Thomson's (Lord Kelvin's) (Frame and Needles). Compass (Frame and Needles).
and west; the 32 points with half and quarter points are seen immediately within the degrees. The north point is marked with a fleur de lis, and the principal points, N.E., E., S.E., &c., with their respective names, whilst the intermediate points in the figure have also their names engraved for present information. The arc contained between any two points is 11° 15'. The mica card is generally mounted on a brass framework, F F, with a brass cap, C, fitted with a sapphire centre and carrying four magnetized needles, N, N, N, N, as in fig. 2. The more modern form of card consists of a broad ring of paper marked with degrees and points, as in fig. 1, attached to a frame like that in fig. 3, where an outer aluminium ring, A A, is connected by 32 radial FIG. 4. - Section of Thomson's Compass Bowl. C, aluminium cap with sapphire centre; N, N', needles; P, pivot stem with pivot.
silk threads to a central disk of aluminium, in the centre of which is a round hole designed to receive an aluminium cap with a highly polished sapphire centre worked to the form of an open cone. To direct the card eight short light needles, N N, are suspended by silk threads from the outer ring. The magnetic axis of any system of needles must exactly coincide with the axis passing through the north and south points of the card. Single needles are never used, two being the least number, and these so arranged that the moment of inertia about every diameter of the card shall be the same. The combination of card, needles and cap is generally termed "the card"; on the continent of Europe it is called the "rose." The section of a compass bowl in fig. 4 shows the mounting of a Thomson card on its pivot, which in common with the pivots of most other compasses is made of brass, tipped with osmium-iridium, which although very hard can be sharply pointed and does not corrode.
A Fig. 4 shows the general arrangement of mounting all compass cards in the bowl. In fig. 5 another form of compass called a liquid or spirit compass is shown partly in section. The card nearly floats in a bowl filled with distilled water, to which 35% of alcohol is added to prevent freezing; the bowl is hermetically sealed with pure india-rubber, and a corrugated expansion chamber is attached to the bottom to allow for the expansion and contraction of the liquid. The card is a mica disk, either painted as in fig. i, or covered with linen upon which the degrees and points are printed, the needles being enclosed in brass.
Great steadiness of card under severe shocks and vibrations, combined with a minimum of friction in the cap and pivot, is obtained with this compass. All compasses are fitted with a gimbal ring to keep the bowl and card level under every circumstance of a ship's motion in a seaway, the ring being connected with the binnacle or pedestal by means of journals or knife edges. On the inside of every compass bowl a vertical black line is drawn, called the "lubber's point," and it is imperative FIG. 5. - Liquid Compass.
N, Hole for filling, with screw plug.
0, 0, Magnetic needles.
P, Buoyant chamber.
when Q, Iridium pivct.
R, Sapphire cap.
S, Mica card.
that when the compass is placed in the binnacle the line joining the pivot and the lubber's point be parallel to the keel of the vessel. Thus, when a degree on the card is observed opposite the lubber's point, the angle between the directior. in which the ship is steering and the north point of the compass or course is at once seen; and if the magnetic variation and the disturbing effects of the ship's iron are known, the desired angle between the ships's course and the geographical meridian can be computed. In every ship a position is selected for the navigating or standard compass as free from neighbouring iron as possible, and by this compass all courses are shaped and bearings taken. It is also provided with an azimuth circle or mirror and a shadow pin or style placed in the centre of the glass cover, by either of which the variable angle between the compass north and true north, called the "total error," or variation and deviation combined, can be observed. The binnacles or pedestals for compasses are generally constructed of wood about 45 in. high, and fitted to receive and alter at pleasure the several magnet and soft iron correctors. They are also fitted with different forms of suspension in which the compass is mounted to obviate the mechanical disturbance of the card caused by the vibration of the hull in ships driven by powerful engines.
The effects of the iron and steel used in the construction of ships upon the compass occupied the attention of the ablest physicists of the i 9th century, with results which enable navigators to conduct their ships with perfect safety. The hull of an iron or steel ship is a magnet, and the distribution of its magnetism depends upon the direction of the ship's head when building, this result being produced by induction from the earth's magnetism, developed and impressed by the hammering of the plates and frames during the process of building. The disturbance of the compass by the magnetism of the hull is generally modified, sometimes favourably, more often un favourably, by the magnetized fittings of the ship, such as masts, conning towers, deck houses, engines and boilers. Thus in every ship the compass needle is more or less subject to deviation differing in amount and direction for every azimuth of the ship's head. This was first demonstrated by Commander Matthew Flinders by experiments made in H.M.S. "Investigator" in 1800-1803, and in 1810 led that officer to introduce the practice of placing the ship's head on each point of the compass, and noting the amount of deviation whether to the east or west of the magnetic north, a process which is in full exercise at the present day, and is called "swinging ship." When speaking of the magnetic properties of iron it is usual to adopt the terms "soft" and "hard." Soft iron is iron which becomes instantly magnetized by induction when exposed to any magnetic force, but has no power of retaining its magnetism. Hard iron is less susceptible of being magnetized, but when once magnetized it retains its magnetism permanently. The term "iron" used in these pages includes the "steel" now commonly employed in shipbuilding. If an iron ship be swung when upright for deviation, and the mean horizontal and vertical magnetic forces at the compass positions be also observed in different parts of the world, mathematical analysis shows that the deviations are caused partly by the permanent magnetism of hard iron, partly by the transient induced magnetism of soft iron both horizontal and vertical, and in a lesser degree by iron which is neither magnetically hard nor soft, but which becomes magnetized in the same manner as hard iron, though it gradually loses its magnetism on change of conditions, as, for example, in the case of a ship, repaired and hammered in dock, steaming in an opposite direction at sea. This latter cause of deviation is called sub-permanent magnetism. The horizontal directive force on the needle on board is nearly always less than on land, sometimes much less, whilst in armour-plated ships it ranges from 8 to 2 when the directive force on land= 1o. If the ship be inclined to starboard or to port additional deviation will be observed, reaching a maximum on north and south points, decreasing to zero on the east and west points. Each ship has its own magnetic character, but there are certain conditions which are common to vessels of the same type.
Instead of observing the deviation solely for the purposes of correcting the indications of the compass when disturbed by the iron of the ship, the practice is to subject all deviations to mathematical analysis with a view to their mechanical correction. The whole of the deviations when the ship is upright may be expressed nearly by five co-efficients, A. B, C, D, E. Of these A is a deviation constant in amount for every direction of the ship's head. B has reference to horizontal forces acting in a longitudinal direction in the ship, and caused partly by the permanent magnetism of hard iron, partly by vertical induction in vertical soft iron either before or abaft the compass. C has reference to forces acting in a transverse direction, and caused by hard iron.
D is due to transient induction in horizontal soft iron, the direction of which passes continuously under or over the compass.
E is due to transient induction in horizontal soft iron unsymmetrically placed with regard to the compass. When data of this character have been obtained the compass deviations may be mechanically corrected to within i° - always adhering to the principal that "like cures like." Thus the part of B caused by the permanent magnetism of hard iron must be corrected by permanent magnets horizontally placed in a fore and aft direction; the other part caused by vertical soft iron by means of bars of vertical soft iron, called Flinders bars, before or abaft the compass. C is compensated by permanent magnets athwartships and horizontal; D by masses of soft iron on both sides of the compass, and generally in the form of cast-iron spheres, with their centres in the same horizontal plane as the needles; E is usually too small to require correction; A is fortunately rarely of any value, as it cannot be corrected. The deviation observed when the ship inclines to either side is due - (i) to hard iron acting vertically upwards or downwards; (2) to vertical soft iron immediately below the compass; (3) to vertical induction in horizontal soft iron when inclined. To compensate (1) A, Bowl, partly in section.
B, Expansion chamber. D, The glass.
G, Gimbal ring.
L, Nut to expand chamber filling bowl.
M, Screw connector.
vertical magnets are used; (3) is partly corrected by the soft iron correctors of D; (2) and the remaining part of (3) cannot be conveniently corrected for more than one geographical position at a time. Although a compass may thus be made practically correct for a given time and place, the magnetism of the ship is liable to changes on changing her geographical position, and especially so when steaming at right angles or nearly so to the magnetic meridian, for then sub-permanent magnetism is developed in the hull. Some vessels are more liable to become sub-permanently magnetized than others, and as no corrector has been found for this source of deviation the navigator must determine its amount by observation. Hence, however carefully a compass may be placed and subsequently compensated, the mariner has no safety without constantly observing the bearings of the sun, stars or distant terrestrial objects, to ascertain its deviation. The results of these observations are entered in a compass journal for future reference when fog or darkness prevails.
Every compass and corrector supplied to the ships of the British navy is previously examined in detail at the Compass Observatory established by the admiralty at Deptford. A trained observer acting under the superintendent of compasses is charged with this important work. The superintendent, who is a naval officer, has to investigate the magnetic character of the ships, to point out the most suitable positions for the compasses when a ship is designed, and subsequently to keep himself informed of their behaviour from the tin g e of the ship's first trial. A museum containing compasses of various types invented during the 19th century is attached to the Compass Observatory at Deptford.
The mariner's compass during the early part of the 19th century was still a very imperfect instrument, although numerous inventors had tried to improve it. In 1837 the Admiralty Compass Committee was appointed to make a scientific investigation of the subject, and propose a form of compass suitable alike for azimuth and steering purposes. The committee reported in July 1840, and after minor improvements by the makers the admiralty compass, the card of which is shown in figs. I and 2, was adopted by the government. Until 1876, when Sir William Thomson introduced his patent compass, this compass was not only the regulation compass of the British navy, but was largely used in other countries in the same or a modified form. The introduction of powerful engines causing serious vibration to compass cards of the admiralty type, coupled with the prevailing desire for larger cards, the deviation of which could also be more conveniently compensated, led to the gradual introduction of the Thomson compass. Several important points were gained in the latter: the quadrantal deviation could be finally corrected for all latitudes; frictional error at the cap and pivot was reduced to a minimum, the average weight of the card being 200 grains; the long free vibrational period of the card was found to be favourable to its steadiness when the vessel was rolling. The first liquid compass used in England was invented by Francis Crow, of Faversham, in 1813. It is said that the idea of a liquid compass was suggested to Crow -by the experience of the captain of a coasting vessel whose compass card was oscillating wildly until a sea broke on board filling the compass bowl, when the card became steady. Subsequent improvements were made by E. J. Dent, and especially by E. S. Ritchie, of Boston, Massachusetts. In 1888 the form of liquid compass (fig. 5) now solely used in torpedo boats and torpedo boat destroyers was introduced. It has also proved to be the most trustworthy compass under the shock of heavy gun fire at present available. The deflector is an instrument designed to enable an observer to reduce the deviations of the compass to an amount not exceeding 2 0 during fogs, or at any time when bearings of distant objects are not available. It is certain that if the directive forces on the north, east, south and west points of a compass are equal, there can be no deviation. With the deflector any inequality in the directive force can be detected, and hence the power of equalizing the forces by the usual soft iron and magnet correctors. Several kinds of deflector have been invented, that of Lord Kelvin (Sir William Thomson) being the simplest, but Dr Waghorn's is also very effective. The use of the deflector is generally confined to experts.
The Magnetism of Ships. 1814 Flinders first showed (see Flinders's Voyage, vol. ii. appx. ii.) that the abnormal values of the variation observed in the wood-built ships of his day was due to deviation of the compass caused by the iron in the ship; that the deviation was zero when the ship's head was near the north and south points; that it attained its maximum on the east and west points, and varied as the sine of the azimuth of the ship's head reckoned from the zero points. He also described a method of correcting deviation by means of a bar of vertical iron so placed as to correct the deviation nearly in all latitudes. This bar, now known as a "Flinders bar," is still in general use. In 1820 Dr T. Young (see Brande's Quarterly Journal, 1820) investigated mathematically the magnetism of ships. In 1824 Professor Peter Barlow (1776-1862) introduced his correcting plate of soft iron. Trials in certain ships showed that their magnetism consisted partly of hard iron, and the use of the plate was abandoned. In 1835 Captain E. J. Johnson, R.N., showed from experiments in the iron steamship "Garry Owen" that the vessel acted on an external compass as a magnet. In 1838 Sir G. B. Airy magnetically examined the iron steamship "Rainbow" at Deptford, and from his mathematical investigations (see Phil. Trans., 1839) deduced his method of correcting the compass by permanent magnets and soft iron, giving practical rules for the same in 1840. Airy's and Flinders's correctors form the basis of all compass correctors to this day. In 1838 S. D. Poisson published his Memoir on the Deviations of the Compass caused by the Iron in a Vessel. In this he gave equations resulting from the hypothesis that the magnetism of a ship is partly due to the permanent magnetism of hard iron and partly to the transient induced magnetism of soft iron; that the latter is proportional to the intensity of the inducing force, and that the length of the needle is infinitesimally small compared to the distance of the surrounding iron. From Poisson's equations Archibald Smith deduced the formulae given in the Admiralty Manual for Deviations of the Compass (1st ed., 1862), a work which has formed the basis of numerous other manuals since published in Great Britain and other countries. In view of the serious difficulties connected with the inclining of every ship, Smith's formulae for ascertaining and providing for the correction of the heeling error with the ship upright continue to be of great value to safe navigation. In 1855 the Liverpool Compass Committee began its work of investigating the magnetism of ships of the mercantile marine, resulting in three reports to the Board of Trade, all of great value, the last being presented in 1861.
See also Magnetism, and Navigation; articles on Magnetism of Ships and Deviations of the Compass, Phil. Trans., 1839-1883, Journal United Service Inst., 1859-1889, Trans. Inst. Na y. Archit., 1860- 1861-1862 , Report of Brit. Assoc., 1862, London Quarterly Rev., 1865; also Admiralty Manual, edit. 1862- 1863-1869 -1893-1900; and Towson's Practical Information on Deviations of the Compass (1886). (E. W. C.) History of the Mariner's Compass. The discovery that a lodestone, or a piece of iron which has been touched by a lodestone, will direct itself to point in a north and south position, and the application of that discovery to direct the navigation of ships, have been attributed to various origins. The Chinese, the Arabs, the Greeks, the Etruscans, the Finns and the Italians have all been claimed as originators of the compass. There is now little doubt that the claim formerly advanced in favour of the Chinese is ill-founded. In Chinese history we are told how, in the sixty-fourth year of the reign of Hwang-ti (2634 B.C.), the emperor Hivan-yuan, or Hwang-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. (Julius Klaproth, Lettre a M. le Baron Humboldt sur l'invention de la boussole, Paris, 1834. See also Mailla, Histoire gdndrale de la Chine, tom. i. p. 316, Paris, 1777.) But, as other versions of the story show, this account is purely mythical. For the south-pointing chariots are recorded to have been first devised by the emperor Hian-tsoung (A.D. 806-820); and there is no evidence that they contained any magnet. There is no genuine record of a Chinese marine compass before A.D. 1297, as Klaproth admits. No sea-going ships were built in China before 139 B.C. The earliest allusion to the power of the lodestone in Chinese literature occurs in a Chinese dictionary, finished in A.D. 121, where the lodestone is defined as "a stone with which an attraction can be given to a needle," but this knowledge is no more than that existing in Europe at least five hundred years before. Nor is there any nautical significance in a passage which occurs in the Chinese encyclopaedia, Poei-wen-yun-fou, in which it is stated that under the Tsin dynasty, or between A.D. 265 and 419, "there were ships indicating the south." The Chinese, Sir J. F. Davis informs us, once navigated as far as India, but their most distant voyages at present extend not farther 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. Sir G. L. 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 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 has been contended 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. G. 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 lodestone 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 lodestone may have been added to the original treatise by the Arabian translators.
Dr W. Robertson asserts (Historical Disquisition concerning Ancient India, p. 227) that the Arabs, Turks and Persians have no original name for the compass, it being called by them Bossola, the Italian name, which shows that the thing signified is foreign to them as well as the word. The Rev. G. P. Badger has, however, pointed out (Travels of Ludovico di Varthema, trans. J. W. Jones, ed. G. P. Badger, Hakluyt Soc., 1863, note, pp. 31 and 32) that the name of Bushla or Busba, from the Italian Bussola, though common among Arab sailors in the Mediterranean, is very seldom used in the Eastern seas, - Dairah and Beit el-Ibrah (the Circle, or House of the Needle) being the ordinary appellatives in the Red Sea, whilst in the Persian Gulf Kiblah-n¢meh is in more general use. Robertson quotes Sir J. Chardin as boldly asserting "that the Asiatics are beholden to us for this wonderful instrument, which they had from Europe a long time before the Portuguese conquests. For, first, their compasses are exactly like ours, and they buy them of Europeans as much as they can, scarce daring to meddle with their needles themselves. Secondly, it is certain that the old navigators only coasted it along, which I impute to their want of this instrument to guide and instruct them in the middle of the ocean.. .. I have nothing but argument to offer touching this matter, having never met with any person in Persia or the Indies to inform me when the compass was first known among them, though I made inquiry of the most learned men in both countries. I have sailed from the Indies to Persia in Indian ships, when no European has been aboard but myself. The pilots were all Indians, and they used the forestaff and quadrant for their observations. These instruments they have from us, and made by our artists, and they do not in the least vary from ours, except that the characters are Arabic. The Arabs are the most skilful navigators of all the Asiatics or Africans; but neither they nor the Indians make use of charts, and they do not much want them; some they have, but they are copied from ours, for they are altogether ignorant of perspective." The observations of Chardin, who flourished between 1643 and 1713, cannot be said to receive support from the testimony of some earlier authorities. That the Arabs must have been acquainted with the compass, and with the construction and use of charts, at a period nearly two centuries previous to Chardin's first voyage to the East, may be gathered from the description given by Barros of a map of all the coast of India, shown to Vasco da Gama by a Moor of Guzerat (about the 15th of July 1498), in which the bearings were laid down "after the manner of the Moors," or "with meridians and parallels very small (or close together), without other bearings of the compass; because, as the squares of these meridians and parallels were very small, the coast was laid down by these two bearings of N. and S., and E. and W., with great certainty, without that multiplication of bearings of the points of the compass usual in our maps, which serves as the root of the others." Further, we learn from Osorio that the Arabs at the time of Gama "were instructed in so many of the arts of navigation, that they did not yield much to the Portuguese mariners in the science and practice of maritime matters." (See The Three Voyages of Vasco da Gama, Hakluyt Soc., 1869; note to chap. xv. by the Hon. H. E. J. Stanley, p. 138.) Also the Arabs that navigated the Red Sea at the same period are shown by Varthema to have used the mariner's chart and compass (Travels, p. 31) .
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 Barlowe's Navigator's Supply, published in 1597, we read:- "Some fewe yeeres since, it so fell out that I had severall conferences with two East Indians which were brought into England by master Candish [[[Thomas Cavendish (Candish)|Thomas Cavendish]]], and had learned our language: The one of them was of Mamillia [[[Manila]]] 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, Lettre, p. 57). E. Wiedemann, in Erlangen Sitzungsberichte (1904, p. 33 o), translates the phrase given above as splinter of wood, by the term wooden cross. 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. 2 49). We have already seen that the Chinese as late as the end of the 8th century made voyages with compasses on which but little reliance could be placed; and it may perhaps be assumed that the compasses early used in the East were mostly too imperfect to be of much assistance to navigators, and were therefore often dispensed with on customary routes. The Arab traders in the Levant certainly used a floating compass, as did the Italians before the introduction of the pivoted needle; the magnetized piece of iron being floated upon a small raft of cork or reeds in a bowl of water. The Italian name of calamita, which still persists, for the magnet, and which literally signifies a frog, is doubtless derived from this practice.
The simple water-compass is said to have been used by the Coreans so late as the middle of the r8th century; and Dr T. Smith, writing in the Philosophical Transactions for 1683-1684, says of the Turks (p. 439), "They have no genius for Seavoyages, and consequently are very raw and unexperienced in the art of Navigation, scarce venturing to sail out of sight of land. I speak of the natural Turks, who trade either into the black Sea or some part of the Morea, or between Constantinople and Alexandria, and not of the Pyrats of Barbary, who are for the most part Renegado's, and learnt their skill in Christendom.. .. The Turkish compass consists but of 8 points, the four Cardinal and the four Collateral." That the value of the compass was thus, even in the latter part of the r 7th century, so imperfectly recognized in the East may serve to explain how in earlier times that instrument, long after the first discovery of its properties, may have been generally neglected by navigators.
The Arabic geographer, Edrisi, who lived about r roo, 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 De utensilibus, written by Alexander Neckam in the r 2th 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 rerum, 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" (W. Chappell, Nature, No. 346, June '5,1876). 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 r3th century, by Guiot de Provins, wherein we are told that through the magnet (la manette or l'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. litteraire de la France, tom. ix. p. 199; Barbazan, Fabliaux, torn. ii. p. 328). Cardinal Jacques de Vitry, bishop of Acon in Palestine, in his History (cap. 89), written about the year 1218, speaks of the magnetic needle as "most necessary for such as sail the sea"; 1 and another French crusader, his contemporary, Vincent de Beauvais, states that the adamant (lodestone) is found in Arabia, and mentions a method of using a needle magnetized by it which is similar to that described by Kibdjaki. In 1248 Hugo de Bercy notes a change in the construction of compasses, which are now supported on two floats in a glass cup. From quotations given by Antonio Capmany (Questiones Criticas) from the De contemplatione of Raimon Lull, of the date 1272, it appears that the latter was well acquainted with the use of 1 Adamas in India reperitur. .. Ferrum occulta quadam natura ad se trahit. Acus ferrea postquam adamantem contigerit, ad stellam septentrionalem. .. semper convertitur, unde valde necessarius est navigantibus in mari.
the magnet at sea; 2 and before the middle of the r3th century Gauthier d'Espinois alludes to its polarity, as if generally known, in the lines: "Tous autresi comme l'aimant decoit [detourne] L'aiguillette par force de vertu, A ma dame tor le mont [monde] retenue Qui sa beaute connoit et apercoit." Guido Guinizzelli, a poet of the same period, writes: - "In those parts under the north are the mountains of lodestone, which give the virtue to the air of attracting iron; but because it [the lodestone] 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." 3 Brunetto Latini also makes reference to the compass in his encyclopaedia Livres dou tre. sor, composed about r 260 (Livre i. pt. ii. ch. cxx.): - "Por ce nagent li marinier a l'enseigne des estoiles qui i sont, que it apelent tramontaines, et les gens qui sont en Europe et es parties deca nagent a la tramontaine de septentrion, et li autre nagent a cele de midi. Et qui n'en set la verite, praigne une pierre d'aimant, et troverez que ele a ij faces: l'une qui gist vers l'une tramontaine, et l'autre gist vers l'autre. Et a chascune des ij faces la pointe d'une aguille vers cele tramontaine a cui cele face gist. Et por ce seroient li marinier deceu se it ne se preissent garde" (p. 147, Paris edition, 1863). Dante (Paradiso, xii. 28-30) mentions the pointing of the magnetic needle toward the pole star. In Scandinavian records there is a reference to the nautical use of the magnet in the Hauksbok, the last edition of the LandndmabOk (Book of the Colonization of Iceland): - "Floki, son of Vilgerd, instituted a great sacrifice, and consecrated three ravens which should show him the way (to Iceland); for at that time no men sailing the high seas had lodestones up in northern lands." Haukr Erlendsson, who wrote this paragraph about 1300, died in 1334; his edition was founded on material in two earlier works, that of Styrmir Karason (who died 1245), which is lost, and that of Hurla Thordson (died 1284) which has no such paragraph. All that is certain is a knowledge of the nautical use of the magnet at the end of the r3th century. From T. Torfaeus we learn that the compass, fitted into a box, was already in use among the Norwegians about the middle of the 13th century (Hist. rer. Norvegicarum, iv. c. 4, p. 345, Hafniae, 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 Barbour writing in 1375 informs us, "na nedill had na stane," but steered by a fire on the shore. Roger Bacon (Opus majus and Opus minus, 1266-1267) was acquainted with the properties of the lodestone, and wrote that if set so that it can turn freely (swimming on water) it points toward the poles; but he stated that this was not due to the pole-star, but to the influence of the northern region of the heavens.
The earliest unquestionable description of a pivoted compass is that contained in the remarkable Epistola de magnete of Petrus Peregrinus de Maricourt, written at Lucera in 1269 to Sigerus de Foncaucourt. (First printed edition Augsburg, 1558. See also Bertelli in Boncompagni's Bollettino di bibliografia, t. i., or S. P. Thompson in Proc. British Academy, vol. ii.) Of this work twenty-eight MSS. exist; seven of them being at Oxford. The first part of the epistle deals generally with magnetic attractions and repulsions, with the polarity of the stone, and with the supposed influence of the poles of the heavens upon the poles of the stone. In the second part Peregrinus describes first an improved floating compass with fiducial line, a circle graduated with 90 degrees to each quadrant, and provided with movable sights for taking bearings. He then describes a new compass with a needle thrust through a pivoted axis, placed in a box with transparent cover, cross index of brass or silver, divided circle, and an external "rule" or alhidade provided with a pair of sights. In the Leiden MS. of this work, which for long was erroneously ascribed to one Peter Adsiger, is a spurious passage, long believed to mention the variation of the compass.
2 Sicut acus per naturam vertitur ad septentrionem dum sit tacta a magnete. - Sicut acus nautica dirigit marinarios in sua navigatione.
Ginguene, Hist. lit. de l'Italie, t. i. p. 413.
Prior to this clear description of a pivoted compass by Peregrinus in 1269, the Italian sailors had used the floating magnet, probably introduced into this region of the Mediterranean by traders belonging to the port of Amalfi, as commemorated in the line of the poet Panormita: "Prima dedit nautis usum magnetis Amalphis." This opinion is supported by the historian Flavius Blondus in his Italia illustrate, written about 1450, who adds that its certain origin is unknown. In 1511 Baptista Pio in his Commentary repeats the opinion as to the invention of the use of the magnet at Amalfi as related by Flavius. Gyraldus, writing in 1540 (Libellus de re nautica), misunderstanding this reference, declared that this observation of the direction of the magnet to the poles had been handed down as discovered "by a certain Flavius." From this passage arose a legend, which took shape only in the 17th century, that the compass was invented in the year 1302 by a person to whom was given the fictitious name of Flavio Gioja, of Amalfi.
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 kingdome of Naples, 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, 1 we need only quote the words of Sir H. Yule (Book of Marco Polo) " Respecting the mariner's compass and gunpowder, I 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 compass card was added is a matter of conjecture. Certainly the Rosa Ventorum, or Wind-rose, is far older than the compass itself; and the naming of the eight principal "winds" goes back to the Temple of the Winds in Athens built by Andronicus Cyrrhestes. The earliest known wind-roses on the portulani or sailing charts of the Mediterranean pilots have almost invariably the eight principal points marked with the initials of the principal winds, Tramontano, Greco, Levante, Scirocco, Ostro, Africo (or Libeccio), Ponente and Maestro, or with a cross instead of L, to mark the east point. The north point, indicated in some of the oldest compass cards with a broad arrow-head or a spear, as well as with a T for Tramontano, gradually developed by a combination of these, about 1492, into a fleur de lis, still universal. The cross at the east continued even in British compasses till about 1700. Windroses with these characteristics are found in Venetian and Genoese charts of early 14th century, and are depicted similarly by the Spanish navigators. The naming of the intermediate subdivisions making up the thirty-two points or rhumbs of the compass card is probably due to Flemish navigators; but they were recognized even in 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 English Text Soc., London, 1872). The mounting of the card upon the needle or "flie," so as to turn with it, is probably of Amalphian origin. Da Buti, the Dante commentator, in 1380 says the sailors use a compass at the middle of which is pivoted a wheel of light paper to turn on its pivot, on which wheel the needle is fixed and the star (wind-rose) painted. The placing of the card at the bottom of the box, fixed, below the needle, was practised by the compassmakers of Nuremberg in the 16th century, and by Stevinus of Bruges about 1600. The gimbals or rings for suspension hinged at right-angles to one another, have been erroneously attributed to Cardan, the proper term being cardine, that is hinged or pivoted. The earliest description of them is about 1604. The term binnacle, originally bittacle, is a corruption of the Portuguese abitacolo, to denote the housing enclosing the compass, probably originating with the Portuguese navigators.
The improvement of the compass has been but a slow process. 1 "According to all the texts he returned to Venice in 1295 or, as is more probable, in 1296." - Yule.
The Libel of English Policie, a poem of the first half of the 15th century, says with reference to Iceland (chap. x.) "Out of Bristowe, and costes many one, Men haue practised by nedle and by stone Thider wardes within a litle while." Hakluyt, Principal Navigations, p. 201 (London, 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 Peter Barlow reported to the Admiralty that half the compasses in the British Navy were mere lumber and ought to be destroyed. He introduced a pattern having four or five parallel straight strips of magnetized steel fixed under a card, a form which remained the standard admiralty type until the introduction of the modern Thomson (Kelvin) compass in 1876. (F. H. B.; S. P. T.)
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Bibliography Information
Chisholm, Hugh, General Editor. Entry for 'Compass'. 1911 Encyclopedia Britanica. https://www.studylight.org/encyclopedias/eng/bri/c/compass.html. 1910.
