By Staff-Commander F. J. EVANS, R.N., F.R.S., Superintendent of Compasses to the Admiralty.

[IN the 47th Number of this Journal, when giving a drawing and a short description of the Fluid Compass supplied by this Institution to its life-boats, we stated that we hoped in a future Number to give an Article on the Mariner's Compass by a gentleman scientifically acquainted with it. By the aid of Commander Evans, R.N., Superintendent of the Compass Department of the Admiralty, who has kindly furnished an interesting Paper on the subject, we are now enabled to fulfil our intentions. Connected as the NATIONAL LIFE-BOAT INSTITUTION is with the interests of this country, in all that pertains to the security of life and property, the pages of its Journal have been deemed a fitting place for a popular Article on the Mariner's Compass.

All classes of the seafaring community, whether long voyage or coasting sailors, yachtsmen, fishermen, or the hardy boatmen of our coasts, have a direct interest in, and some acquaintance with, this familiar sea-instrument; yet it would appear as if this wide familiarity had engendered some indifference to its requirements and functions, and consequent ignorance of its remarkable properties and the laws which govern its action.

It would be beyond the scope of this Article to more than briefly touch on the governing laws to which we have alluded, but it may prove of interest, and perhaps be attended with good results, to place before our nautical readers some account of the essentials of a good working compass; to notice the worthy labours that for a long series of years have been bestowed on it theoretically and practically, as also some of the crude current ideas as to the fundamental principles on which its action depends ; and to detail in general such points in its construction as may be useful in practice, prefacing the whole by a concise retrospect of what is known of its history by record or tradition.

Wrapt as the early history of the Mariner's Compass is in obscurity, there is sufficient evidence to prove that at a very remote period among the Eastern nations the directive power of magnetized iron was known, and that it was turned, by the Chinese, to purposes of distant travel, if not to extended navigation. The time of its introduction among the Western nations of Europe is comparatively recent; the merit of the invention of the compass in its present arrangement of box, bowl, and supporting pivot, being assigned to a Neapolitan citizen, about the year 1302; but recent literary research indicates that it must have been in use, under similar conditions, at least a century earlier, by the mariners of England and France.

Between the remote date recorded in the Chinese annals (said to be about 2600 years B.C.) of the application of the freely-suspended magnet to purposes of travel and that just given, little or nothing is known of its history. The successive powerful nations that existed near the shores of the Mediterranean sea have left no records of its em-ployment, and we may certainly draw the inference that in the lengthened and circuitous voyage of St. Paul, which resulted in shipwreck on the Island of Malta, the " shipmen" had not the advantage or consolation to be derived from this guiding monitor.

By some it may be considered puerile to seek after records which add so little to our real knowledge, but considering the powerful aid the Mariner's Compass has rendered to civilization, and the material progress that has been made in the well-1teing of mankind from the days of Columbus and Vasco de Gama, by opening up the navigation of vast and distant oceans, and the consequent discovery of rich and fertile lands; the interest of the intelligent seaman cannot fail to be enlisted towards whatever relates to so priceless an auxiliary to his labours.

It is somewhat remarkable that the compass, valuable as it is to us, and honoured in song as it has been from the days of the Troubadours to those of Dibdin—the sailors' bard—has not at all periods received the same meed of honour from those most interested in its use. In the 17th century several treatises were written relating to the discovery of longitude, to be attained by magnetic observations of the dip and variation of the compass-needle: from the interest created at the time by these views, we may infer that at that period the value of the compass to navigation was thoroughly appreciated, and we find that in immediate connection with the development of certain magnetic laws directly affecting it, a special voyage of research to the South Atlantic Ocean was undertaken by the illustrious HALLET under the direction of the British Government in 1701.

In the middle and towards the close of the 18th century, much attention was paid to the fabrication of magnets, and the art of infusing high magnetic power into them had attained a great degree of excellence.

Notwithstanding this progress, we find, in the beginning of the 19th century, the celebrated navigator Flinders describing the compasses of the Navy as " the worst-constructed instruments of any carried to sea;" and in 1820 that able philosopher, Peter Barlow, in an official report to the Board of Admiralty, on the compasses of the Royal Navy, stated that more than one-half of those he had examined (150) " should be considered as mere lumber, and ought to be destroyed."* It would be an interesting subject of inquiry to trace the causes leading to the decline of the compass in the estimation of seamen which brought about such a falling off in its fabrication ; we can alone now shadow forth one or two probable ones. In the time of our scientific navigators of the last century, Cook, Vancouver, Phipps, and others, great attention was devoted to the determination of purely magnetic observations, partly with the practical view of the results being ultimately useful (thus reviving the old idea) in obtaining the longitude; the dip of the needle, for example, was frequently observed at sea, and the variation of the compass was certainly determined in many distant parts of the world with considerable accuracy, as is verified by recent observation and investigation. Singularly enough, the discrepancies in the variation of the compass, as then observed at sea, under different circumstances of the position of the instrument, and the direction of the ship's head, and which we can now trace to the action of the iron in the ship magnetized by induction from the earth, were considered as due to inherent errors of manufacture, and its character for accuracy of course looked on with suspicion. The art of navigating by lunars and chronometers was now cultivated by the higher class of seamen, the check on the compass was consequently more perfect, and the navigator was again more independent of it. Among the general mass the golden rule of the " three L's," or strict attention to the lead, latitude, and look-out, was the common formula of navigation, without even an allusion to the poet's " unerring guide." The compass was now probably at its lowest ebb in the tide of professional opinion, for we actually find it * It is scarcely necessary to say that this state of things BO longer exists; from the time of Bisuow's Report UveTe has been progressive improvement, and there is ample testimony from many disinterested and leading authorities that the chief compasses of the Royal Navy have attained a high degree of excellence; and, indeed, have been adopted as models by other first-rate navies of the world.

treated as a hardware article, specially manufactured in the Minories and its neighbourhood with other ships' stores, and stowed away indiscriminately with iron hooks and thimbles, deck scrapers, hook-blocks, and other choice miscellanea of the boatswain's storeroom: this is no fanciful picture, but what is well known to those conversant with the naval services little more than a quarter of a century past.

Let us turn to the present day, and take for example what we find recorded in this Journal, at the opening of the year, relating to a compass designed for the Life-boat Institution; it is described as very portable, compact in its details, serviceable in its arrangements, and exact as a philosophical instrument; in fine, " it is found to answer 1 admirably in every respect." Now, although this excellent character cannot be applied to the compasses m general use in the mercantile navy, still much improvement has taken place in late years both in the manufacture and in their treatment on board ship.

The improvement as a sea instrument may in part be traced to the introduction of steam, a vessel being thus enabled to make as much progress on a direct course in a few hours as would formerly have taken days to accomplish; the improved sailing powers also of nearly all classes of ships, and the competition and emulation in making quick passages have further tended to place the compass as an indispensable auxiliary to the sextant and chronometer; greater issues depend on its correct action than in those days when time was of 'little importance to the seaman, and when, on the approach of apprehended danger, the ship's head was turned away from the obstacle, and a more propitious season quietly awaited.

The seaman of to-day, without disregarding the good old " three L's," is obliged to give a more prominent position to his compass.

The progress of our knowledge of terrestrial magnetism, one of the most important branches of physical science, has also been most marked in the last half century.

The extensive (and, so far as the compass is concerned, it is to be feared too often extravagant) introduction of iron into the construction and equipment of ships, which, by increasing the errors of the compass, diminishes materially in some directions of the ship's head its directive power, and thus renders a sluggish compass, or in other words an inferior compass, useless, or even worse than useless, has necessitated not only the employment of compasses of superior manufacture, but also some knowledge of the laws which affect them by the action of the ship's iron: this last is a subject on which we forbear to treat at present, but the resulting principle should not be lost sight of, namely the absolute necessity of a compass of first-rate character forming a part of the equipment of every vessel in which iron enters largely into the fittings.

The question may now be asked—-What are the essentials of a good compass ? Before answering this question, it may be advisable to give some account of the features of a bad compass, and this we shall do by making a few extracts from the Report of the late Professor Barlow on the contract compasses of the Navy in 1820, to which allusion has already been made, and it will be seen how closely his description applies to those of the genuine old Minories' stamp, forming too frequently at the present time the miserable equipment of our coasting craft, and, indeed, of some of our noble foreign trading ships.

Mr. Barlow considered, after his extended examination, " that the causes of error may be reduced, to the three following:— " 1. The errors which naturally appertain to the form of the needles usually employed in those instruments.

" 2. To imperfect workmanship.

" 3. To the manner in which the compasses are kept in store.', " With respect to the imperfections in workmanship, it is needless to enter, into detail. The cards are many of them effiptical, rather than circular; true centering seems to be entirely disregarded, and the pivot capping which ought to be agate, seems in many instances only to be common glass. The balance also in various cards is only preserved by a very liberal distribution of sealing-wax, which increases the weight of the card, and prevents it traversing, par- ticularly where the needle has but slight directive power.

" With respect to the first of the above sources of error, it is to be observed that the needles are commonly of a form approaching very nearly to a parallelogram as shown in the annexed figures, and conse- North.

1 2 3 South.

quently the accuracy of the bearing of the card will depend upon the north and south point of the needle coinciding with the geometrical axis of the figure-as in figure 1.

In this case, if the card be placed with its north and south points corresponding with the axis of the needle, there will be no deviation ; but if, in communicating the magnetic fluid to the needle, the greatest accumulation should be oblique with respect to the axis as in figure 2 and 3, then the card being placed as before, its north point will bear to the east or west of the true magnetic north by a quantity equal to that obliquity." This was proved by unscrewing the cap of one of the needles, and screwing it again on the other side, thereby turning the face of the card downwards, and then suspending it again; the error in deviation was now found to be 4° east instead of 4° west, as originally observed, a circumstance which the Professor " conceives can only be accounted for by supposing the needle to have received its magnetism in a diagonal direction, instead of its being communicated in a line coincident with its geometrical axis. This source of error may, it is obvious, be avoided by suspending the needle edgewise, instead of flatwise." On the third source of error there are the following valuable remarks, which apply well to the conservation on ship-board.

" It is a well-known fact, if two magnets be brought near and parallel to each other, with their poles inverted, or if they be laid across each other, or be in any other irregular manner brought into contact, or within each other's influence, the power of each will be impaired, and perhaps ultimately destroyed. Now, in the store, the boxes containing the cards, &c., are all placed and piled on each other indiscriminately, without any regard being paid to the directions of the needles within them; consequently there is a perpetual decomposition of the magnetic influence going on, which would ultimately derange and destroy the action of the most perfect instrument; and to this cause is doubtless to be attributed the very weak directive force of many of the needles which I examined, as I cannot imagine that any instrument-maker would deliver them in the state in which they now are." The closing paragraph of this Report is so comprehensive, that, at the risk of repetition, we introduce it, adopting' most fully the Professor's views:—"I am aware" (says the Professor) " that many nautical men set a very little value upon the compass; but this, I conceive, arises from the constant defects it is found to exhibit, and not that from its nature it is incapable of rendering them essential service. If, indeed, a lunar or other astronomical observation could be made at all times, this instrument might perhaps be nearly dispensed with; but as it frequently happens that several days pass without such an opportunity presenting itself, the perfection of the compass cannot be an object of indifference; and I cannot help thinking, if this perfection was attained, that a great degree of accuracy might be introduced into the dead reckoning, and many severe and afflicting losses prevented." We now proceed to the consideration of the essential qualities of a good compass.

These we consider to be the combination of great sensibility and stability with simplicity of construction. By sensibility and stability it is to be understood that the needle is freely to submit to the earth's magnetic force, with power sufficent to steadily obey that force under the varying motions of a ship, without the aid of friction or other mechanical impediment; steadiness (or rather sluggishness) produced by the latter causes being obtained, as is now well known, at the expense of accuracy.

The growing demand of late years for an efficient compass has produced—to meet the qualities described—an almost endless variety of forms and arrangements of details, of which the generality are more or less complicated, and, of course, more or less difficult of repair, and costly. Simplicity of construction, so that repairs could be effected by an ordinary skilled mechanic, must be deemed a qualification of merit.

The principal modern improvements may, after all, probably be reduced to the introduction of compound needles, arranged on sound philosophical principles, and in the manufacture and fitting liquid compasses; —by the latter is meant those compasses in which the card and suspension is immersed in fluid, and whose use in any excessive motion of a ship or boat appears to be indispensable. We propose, however, to confine our attention chiefly to the simple form of compass, premising that the essential points of construction are equally applicable to the liquid compass.

The chief points to be attended to in the construction of the Mariner's Compass are: —(1) Great directive power of the needle, with little weight, and consequently little friction on the point of suspension. (2) Permanency of the magnetic power or force in the needle. (3) Accurate adjustment of the several parts of the compass. This comprises:— (a) The magnetic axis of the needle coinciding with the north and south points of the card.

(6) The intersecting point of the axes of the gimbals of the bowl coinciding with the point of suspension of the card.

(c) The accurate centering of the point of suspension within the bowl.

(cC) The perfect impression of the card, so that the centering and marginal divisions are not distorted by shrinking or other causes.

Some of the foregoing points may be usefully reviewed in detail; but as the essence or cardinal virtue of the compass is concentrated in the needle, our principal attention will be directed to the consideration of this wonderful agent.

There are numerous records within the last century of the labours of various philosophers in investigating the best form for compass-needles—their size, solidity, weight, kinds of steel best adapted, and methods of tempering and magnetizing. It would far exceed our limits to relate the various results; we must therefore restrict this part to an enunciation of certain principles, which, from being consistent with known magnetic laws, and further established by experiment and experience, may be received with due confidence.

he question, which is a very important one, as to what form should be given to the needle to produce the most advantageous effect, is thus answered in the language of science: " That form is to be recognized as the most advantageous in which are united the greatest possible magnetic moment, with the smallest possible mass, and the smallest possible moment of inertia." Experiments based on these conditions result in the following;— 1. That narrower magnets are more advantageous than broader.

2. That thinner magnets are more advantageous than thicker.

3. That consequently the most advantageous form is that in which breadth and thickness disappear, and the magnet (or needle) is transformed into a mathematical line—that is, into a so-called linear magnet.

We have thus authority for applying to the needle the simplest of forms; but there is another important result from the experiments which led to the foregoing conclusions, namely, that " there is only one means of obtaining great magnetic strength with trifling weight, viz., by firmly cementing several thin and flat magnets near or upon one another in one system, without their touching each other." There is a limit, however, to the effective combination of several magnets, similar to those just described, which may be thus summed up:— (1) Any single magnet has more proportionate magnetic power than two such magnets combined. (2) A combination of such magnets has more actual magnetic power than any single magnet containing the same quantity of steel in mass. 3. The absolute gain of power by each additional magnet diminishes progressively, and hence a limit to the extent of combination.

We see here the advantage of reducing the weight of the needle by making it as thin as is consistent with strength; increasing its power by the addition of one or more lamina?; or again, multiplying the power by placing two or more such combined needles on the card. The arrangement of a compound system of needles has been received with disfavour by many acknowledged authorities, on the grounds that their similar poles, being so closely adjacent, would in effect mutually destroy their magnetic power. Experience has proved, however, that a remarkable amount of permanency will be found in properly-constructed needles so placed, after the lapse of many years. This objection, practically, therefore does not exist.

The advantage of a compound system of needles over a single needle, in addition to that of greater directive power being obtained with the same weight (and the interference of the pivot-cap with the centre of the needle), are manifold and somewhat remarkable.

The needles can be placed on their edge, whereby there can be no alteration of their magnetic axes (see preceding figure).

By placing two equal parallel needles with their ends 60° apart—t. «., 30° on each side of the north and south line of the card —or, similarly, two pairs of equal parallel needles 30° apart—i.e., 15° and 45° on each side of the north and south line*— the moments of motion about all horizontal axes are equal, and oscillations of the card about any axes—or, in other words, with the ship in motion with her head in any direction—are performed without the " wabbling" motion common to single bar needlecards.

The following remarkable property also exists, which points to the desirability of compass needles, combined as just de- * As in the Admiralty Standard Compass card.

scribed, being furnished to iron ships especially :— When magnets or soft iron are placed as correctors of the larger deviations due to the iron of the ship, unless the needle (where a single bar is employed) be very short, compared to the distance of the disturbing magnet or iron, a deviation is introduced depending on the length of the needle; this deviation disappears with the compound arrangements.

The tendency of late years has been, in particular cases, to considerably increase the length of the compass-needle above that generally adopted of 6 to 7 inches; although we may consider that increase of length gives a proportionate increase of directive force, yet the weight, and consequently the friction, increases proportionally, so that nothing material is thereby gained. There is also this objection, that a perfect long needle is more difficult of manufacture than a perfect short needle, the former being more liable to have " consecutive poles "— that is, the whole of the polarity is not collected at either end, but distributed alternately along the length; this defect occasions great loss of directive power: on the whole, a length not exceeding 6 to 8 inches appears to embrace all the necessary conditions of a good needle. • Polishing the needle of a compass is of no advantage considered magnetically: for general use in all climates, a coat of paint or varnish is, on the whole, preferable.

Among the parts of a compass which in the course of time most affect its correct working are the pivot and cap on which the needle traverses; great care is therefore required both in the selection of the materials —subject as they mutually are to constant friction—and the accuracy of workmanship of those parts. Agates are commonly used for caps, but it has been remarked by a competent authority " that this is the worst of the hard materials that are fitted for pivots of any kind, as it consists of an immense number of thin strata of different degrees of hardness, and which can often be seen only with very powerful microscopes." Rubies and sapphires are now used in the fittings of superior instruments.

Steel pivots, hardened and duly tempered, have now taken the place generally of the old-fashioned iron-spike. To preserve the points from rust, they are, in some first-rate compasses, gilded by the electrical process, and also pointed with a peculiar metal, found with platinum, known as " native alloy," the properties of this metal being remarkable hardness, and freedom from rust under most trying conditions. Pivots for heavy or storm-card are frequently, instead of being pointed, tipped with a rounded ruby; in which case the hollow of the cap is made of gun or speculum metal, highly polished, and accurately adapted to the size and shape of the nitty. With powerful needles, this arrangement works remarkably well. With a pointed pivot, the perfect adaptation of the point to the cavity of the stone in which it works is essential; the stone should also have a high degree of polish. These minutiffi are ' neglected in inferior compasses.

An interesting fact in magnetic science, which bears directly on the efficiency of the compass, is the influence of non-magnetic substances generally in quieting the vibrations of the magnetic needle. Metallic substances have the greatest influence—silver and copper in a very high degree; we 6ad accordingly that when a magnet is vibrated within a ring of copper, the amplitude of the arcs of vibration are sensibly reduced—• although the times of vibration remain the same—and the bar, or needle, tends rapidly to a state of rest.* The comparative tranquillizing effect of copper over wood is very great (about 75 to 1) ; the "bovA, tiaerefore, of a compass with any pretensions to excellence should be constructed of pure copper, of substantial thickness, and the part adjacent to the needle increased in solidity by an extra ring, the ends of the needle being permitted to work as close to the ring as consistent with freedom of motion.

These latter details are based on the assuiaed law of the restrainiEg force of the * Physical research has shown that this is not the result of ordinary magnetic action, but is dependent on the gene, ration of electrical current induced by the magnet whilst la motion In the metallic ring; and is termed Jtfagneto- Elcctric Induction.

copper with a given magnet, being inversely as the squares of the distance from the pole of the bar, and directly as the quantity of copper within its sphere of action.

We have thus sketched the chief details of the Mariner's Compass; and it is obvious that there is required in its most simple construction good and often costly material, combined with a high order of skilled labour, and a knowledge of many mechanical and philosophical principles. We cannot look for more in either of those aids to the seaman, the chronometer and sextant.

An Article on the Mariner's Compass would at the present time be incomplete without some reference to those wild, and often dangerous schemes to the unwary mariner, which are occasionally before the public; professing to render the compass indifferent to the magnetic influence of the iron, of the ship by the interposition of some non-conducting or conducting substance, so that the needle shall point to the magnetic north under all circumstances, and in all places. One of the fundamental laws of magnetism is here overlooked; for the influence of this marvellous and mysterious force is, like that of gravity, exerted through ail bodies without the slightest interruption.;—as also the obvious consideration, that if any body could intercept the action of the ship's iron, it would also intercept the action of the earth's magnetic force on the needle.

SHIPPING.—The entries of British tonnage at ports of the United Kingdom have risen from 7,621,035 tons inwards and 7,699,497 tons outwards in 1S61, to 'i ,Sb&,6aS teas iiwratto smi %, »i i,m tons outwards in 1862. The foreign tonnage fell from 5,458,554 tons inwards and 5,716,555 tons outwards in 1861, to 5,234,451 tons inwards and 5,354,128 tons outwards in 1862. On the registry of the whole British, empire, including the plantations, there were at the close of the year 1862 39,407 vessels of 6,042,096 tons—an increase over the previous year of 539 vessels, and 146,727 tons.

In 1862 there were 1,923 new ships of 451,534 tons built and registered in the United Kingdom and British plantationsr-a greater addition than in 1861 hy 201 vessels and 132,706 tons. Tie number of vessels, British and foreign, which entered ittwtwds and cleared outwards from different ports in the United Kingdom during the past year teas 268,462. They were manned, probably, by 1,610,000 men.