North East;" "South, South West," and "West, South West ;" "South, South East," and "East, South East."

In Plate IX. Miscel. fig. 9 and 10, we have given figures of a compass and compass-card, according to the mariner's afrangement just described, in which only the initials are shewn: the North point being distinguished, as it always is, by a fleur de lys, or some particular indicial ornament. For further particulars, see MARINER'S compass.

We have been the more particular in describing the formation of the compass card, because a perfect knowlege of that important aid is indispensably necessary for all who attempt the study, or follow the practice, of navigation. Under the head of MAGNETISM we have explained the properties of the load-stone, and spoken of the dip of the needle, as well as of the variation which exists between the true and apparent polar directions; as indicated by the compass. Therefore we shall briefly observe, that variation is either Easterly, or Westerly; and, whenever it prevails, must be computed in the reckoning; always making allowance for the difference, and laying down the ship's course accordingly. Thus if a ship sails due North, and that six degrees of Western variation are known to prevail in that part, where the vessel is sailing; instead of sailing due North, as indicated by the compass, the vessel must sail six degrees more Easterly, or, in other words, North half East, i. e. half a point Easterly of North, in which direction the true North point would be found by observation of the heavenly bodies. Currents must also have allowance made for them according to their bearing, or the points to which they run it is self-evident, that if such were not duly ascertained, and set off from the dead reckoning, the ship's place would never be accurately laid down, and destruction would inevitably follow the neglect.

The way, or distance, the ship sails with in the day, is ascertained by means of a small piece of board called the LOG (which see), that being fastened to a thin, but stout line, and lowered over the stern, occasions the line to run off from a large reel. The line being marked at certain distances with small pieces of string, whereon, one, two, three, &c. knots are made, at distances corresponding with the rate per hour, and the persons who superintends the process, having a minute, or a half minute glass; the log is allowed to run the line

from the reel, during such interval; the number of knots, on the proximate string, indicating the number of miles the ship sails within the hour. Hence the techinical term of so many "knots per hour;" or "an eight knot breeze," &c.

The whole world is supposed to be comprized under a circle, which in every direc tion, contains 360 degrees of equal measurement. Such as pass through the meridian of any place, and from North to South, cutting the equator at right angles, are called meridional lines, and are each divided into nine degrees, counting from the line towards the poles respectively: those proceeding to the North are called degrees of North latitude; those towards the South being called degrees of South latitude. In this respect all civilized nations are agreed; but in their estimation of longitude, they generally differ, each taking some parti cular point within their own dominions as zero, and counting 180 degrees East, and as many West; calling the former East longitude, the latter West longitude. Consequently the union of those adverse desig. nations takes place at the antipodes of the zero from which they proceeded; and the moment a vessels passes 180 degrees, either way, she enters upon 179 of the opposite semi-circle, and reckoning the degrees of latitude are equal from the equator to the pole; and each in general measures about 69 of British statute miles. But the degrees of longitude vary greatly; decreasing regularly from the equator to the poles, where they all meet and are as it were an nihilated. The regular declension of the circles of longitude, which are the same as parallels of latitude, may be seen under the head of DIALLING; where in the construction of lines of latitude, their gradual decrease is fully exhibited: see also LoxGITUDE, for a table of longitudes in various latitudes.

A rhumb-line is a right line drawn from the centre of the compass to the horizon, and is named from that point of the horizon it falls upon. The course is the angle which any rhumb-line makes with the meridian, and is sometimes reckoned in degrees, and sometimes in points of the compass; so that if a ship sail upon the second rhumb, or N. N. E. the course is 22° 30', and so for any other. When a ship makes a direct course from one point or port to another, and that there is no current nor any variation of the compass, she sails "on a rhumb," that is, she is guided invariably from one to the

other throughout her course by one point, of the compass, being governed throughout her passage by that line only. This is different from what is called traverse sailing, which arises from adverse winds, or sometimes from currents, and obliges a vessel to change her course occasionally; especially where the vicinity of land renders it necessary to steer at times differently; lest the current, which generally changes from one side or direction to another, should set her against the shore. When the wind is diametrically, or obliquely against a ship's direct course, she must make traverses, i. e. zig zags, which is effected by laying her head as close to the wind as may allow her sails to be filled when close hauled; (see Plate XI. Miscel. fig. 12.) in which A is the place of departure, B the point of destination, from which the wind blows direct, and Ab, bc, c B, &c. the course the ship must steer to arrive at B. Square rigged ships generally can lay within six points of the wind; but sloops, &c. commonly lay up within four points and a half. When working in this manner it is called "beating," or "plying to windward:" when the wind blows straight upon the side of the vessel, it is said to be "on the beam;" when between her side and stern, it is called "a quartering wind," or "on her quarter;" when direct astern, or near it, she is said to be" before the wind," or to "sail large." When the wind from being fair becomes suddenly foul, it is said to "take her aback."

In traverse-sailing the vessel's head is usually turned up "into the wind" when she is "put about." This is called "tacking;" but if, instead of " throwing her up" in that manner, she is allowed to go round from the wind until it comes or is met by her on the other side, it is called "wearing." When she has the wind on her starboard, or right bow, she is said to "have her star board tacks aboard," and vice versa when the larboard, or left, how is to the wind. To know how close a ship will lay to the wind, observe the course she goes on each tack, say north on one, and south-west on the other; divide in the middle, and her course will appear to be west-north-west. But allowance must be made for lee-way, which is the loss made by the impression made on the vessel as she is working to windward; when the wind presses her from the direct line of her course, and occasions her to "drift to leeward." See LEEWAY.

The following is the established rule for VOL. IV.

laying down a traverse course on paper. Having drawn the meridian and parallel of latitude (or east and west line) in a circle representing the horizon of the place, mark in the circumference the place of the wind, that is, the point from which it blows; draw your rhumb passing through the place bound to, and lay thereon the distance of that place from the centre; on each side of the wind lay off in the circumference those points, or degrees, that shew how near the wind the vessel can lie, and draw their rhumbs. Now the first course will be one of these rhumbs, according to the tack the ship first sails upon; when she goes on the other tack, it will be at such an angle as may correspond with her ability to lay near the wind; but, in general, for square rigged vessels the angle should be twelve points, (i. e. six for the distance on each tack, as shewn in fig. 12.) But where the wind is not directly adverse, it would be improper to make the tacks towards both rhumbs of equal duration or length. Therefore that tack should be longest which lays nearest the intended course; the other (i. e. “ the board") should be short, so that the vessel should not go too far from the intention, but adhere as much as may be practicable to the rhumb of her course, as shewn in fig. 13, in which the arrow shews the wind's locality at three points east of the destination B.

To resolve a traverse, is to reduce and bring several courses into one; the courses are known by the compass, the distance by the log: while the dead-reckoning they produce is corrected by daily observation of the sun and other planets whenever opportunity offers.

In constructing figures relating to a ship's course, let the top of the paper always represent the north: your meridian is described perpendicular thereto, and your chart may either be in squares, for degrees, or five or ten degrees, or it may be divided according to the projected tables now in common use (see LONGITUDE), and which is by far the best, as it shews the real distances and bearings, according to the actual positions of places, as proved by observation. In that table the letters D. L. imply the degree of latitude, measured from the equator, either northwards or southwards; in the columns of miles corresponding thereto, you will see how many miles, of sixty to a degree, called geographical miles, are contained in each degree of longitude under such latitudes. Thus, if I would know how Rr

many miles are contained in a degree in latitude 18; I find there are 57.06. Therefore it must be evident, that, as the latitude recedes from the equator, the smaller the degrees of longitude become: hence, if a vessel could sail round the north pole in latitude 80o, where there are only 10° 42′ miles in a degree of latitude, and were to run 123 miles in the twenty-four hours, she would sail ten times round the pole, and indeed round the world, in that time, and see the sun rise and set no less than twelve times!

From this we are satisfied that the old practice of laying down a chart, or map, in square degrees was erroneous in the extreme; and that what is called "Merca. tor's projection," which gives every degree its just and exact value in breadth, at both its northern and its southern extremities, is the only correct and rational mode of description.

We shall now give the reader a few examples under the head of plane sailing, which supposes the earth to be a perfect level, or plane. This is but the application of plane trigonometry to the solution of the several variations; where the hypothenuse, or longest side, is always the rhumb on which the ship's course lies. The perpendicular is the difference of latitude counted on the meridian, and the base the departure (which is either easting or westing) counted from the meridian. The angle opposite the base is that which the ship makes with the meridian: the angle at the perpendicular is the complement of the course; which, taken together, always make 90 degrees, or eight points. When the course is given in degrees, they must be set off from a line of chords of 60, corresponding with the radius of the circle, or quadrant, drawn either easterly or westerly, as the ship's course may be, from the meridian. Where the course is given in points, it may be set down with its corresponding logarithm in points in the calculation, as found in the first page of logarithms in general. In all cases, wherever the complement course is used, the degrees, or points, put down, correspond with the course itself; yet the logarithm belonging to the complement of that course is taken.

Example 1. "Course and distance sailed being given, to find the difference of latitude, and the departure from the meridian." Suppose a ship from the Lizard, in the latitude of 49° 57′ north, sails S. W. by W. 496 miles; required the latitude come to, and

her departure from the meridian. Draw the meridian, or difference of latitude; with the chord of 60° in your compasses, and one foot in C, (fig. 14) describe an arch: take 56° 15', or five points, in your compasses, and lay off that distance upon the arch, from BC towards CA: through the point where it cuts draw the distance CA, upon which set off 496: from A let fall the perpendicular A B, the departure, and it is done. For A B, being measured on the same scale that AC was, will give the departure 412.4, and BC 275.6, for the difference of latitude.

Example 2. "Course and difference of latitude being given to find the distance ran, and the departure from the meridian.” If a ship runs S. E. by E. from 1° 45′ north latitude, and then by observation is in 2° 50′ south latitude, required her distance and departure? As the ship has crossed the line (i. e. the equator), the north latitude 1° 45′ must be added to the south latitude 2° 50′; which makes the difference of latitude 4° 35'. Multiply that by 60, and there appear 275 geographical miles. Now draw BC (fig. 15) equal to 275; and B A, making an angle with BC equal to five points, or 56° 15′: upon C erect the perpendiculars CA, to join BA in A. Then will C A be 112, and A B 496 miles; therefore the ship's run has been 496 miles, and her departure from the meridian 411.6 easterly.

Example 3. "Course and departure being given, to find the distance and the difference of latitude." If a ship sails N. E. by E. ¿ E. from a port in 3° 15′ south latitude until she depart from her first meridian 412 miles, what latitude will she be in? Draw DA (fig. 16), upon which erect the perpendicular A B; draw the line AC, making an angle with AB equal to 64° 41', corresponding with 5 points. At the distance of 412 miles draw DC, parallel to A B, to cut AC in C: through the point C draw BC parallel to A D, to cnt the meridian A B. Thus AC will give 456 miles for the distance run, and A B 195 miles for difference of latitude.

Having said thus much by way of general information, we must refer those readers who are in search of extensive knowledge in the art of navigation to the several treatises which have been written by its professers; among which, we believe, those published by Mr. Nicholson and the late Jolm Hamilton Moore have had the greatest charac ter for utility and general accuracy. With respect to what appertains more to the ex

amination of harbours, coasts, soundings, &c. we refer to SURVEYING.

Under the article QUADRANT the mode of taking observations at sea will be given, for ascertaining the latitude by solar observation.

NAUSEA, in medicine, a reaching, or propensity and endeavour to vomit, arising from a loathing of food, excited by some viscous humour that irritates the stomach.

NAUTILUS, in natural history, a genus of the Vermes Testacea class and order. Shell univalve, divided into several depart. ments, communicating with each other by an aperture. There are more than thirty species, separated into sections. A. Spiral, rounded, with contiguous whorls. B. Spiral, rounded, with separated whorls. C. Elongated and straightish. N. pompilius, inhabits the Indian and African oceans; often very large, and finely variegated with brown flexnous streaks, spots, and marks, under the outer covering, which is white; within of a most beautiful pearly gloss. Of this species, the inhabitants of the east make drinking cups. N. spicula, aperture of the shell orbicular; whorl cylindrical: it inhabits the American and Indian oceans; about an inch in diameter; whitish within, shining like mother-of-pearl; orbicular; the whorls gradually decreasing inwards, the first a little straight; siphon contiguous to the walls of the shells.

NAVY, the fleet or shipping of a prince or state.

The management of the British navy royal, under the Lord High Admiral of Great Britain, is entrusted to principal officers and commissioners of the navy, who hold their places by patent. The principal officers of the navy are four; viz. the Treasurer, whose business it is to receive money out of the exchequer, and to pay all the charges of the navy, by warrant from the principal officers: Comptroller, who attends and comptrols all payment of wages, is to know the rates of stores, to examine and audite all accounts, &c.: Surveyor, who is to know the states of all stores, and see wants supplied, to estimate repairs, charge boatswains, &c. with what stores they receive, and at the end of each voyage to state and audite accounts: Clerk of the Acts, whose business it is to record all orders, contracts, bills, warrants, &c.

The Commissioners of the navy are five: the first executes that part of the Comptroller's duty which relates to the comptrolling the Victuallers' accounts; the second, an

other part of the said Comptroller's duty, relating to the account of the store-keepers of the yard; the third has the direction of the navy at the port of Portsmouth; the fourth has the same at Chatham; and the fifth at Plymouth.

There are also other Commissioners at large, the number more or less, according to the exigencies of public affairs; and since the increase of the royal navy, these have several Clerks under them, with salaries allowed by the King.

The victualling of the royal navy had formerly been undertaken by contract, but is now managed by Commissioners, who hold their office at Somerset House, Strand.

NEBULE, in astronomy. There are spots in the heavens called nebulæ, some of which consist of clusters of telescopic stars, others appear as luminous spots of different forms. The most considerable is one in the midway between the two stars on the blade of Orion's sword, marked by Bayer, discovered in the year 1656 by Huygen's; it contains only seven stars, and the other part is a bright spot upon a dark ground, and appears like an opening into brighter regions beyond.

Dr. Halley and others have discovered nebulæ in different parts of the heavens. In the "Connoisance des Temps," for 1783 and 1784, there is a catalogue of 103 nebulæ, observed by Messier and Mechain. But to Dr. Herschel we are indebted for catalogues of 2000 nebulæ, and clusters of stars, which he himself has discovered. Some of them form a round compact system, others are more irregular, of various forms, and some are long and narrow. The glo. bular systems of stars appear thicker in the middle than they would do if the stars were all at equal distances from each other; they are, therefore, condensed toward the centre. That stars should be thus accidentally disposed is too improbable a supposition to be admitted; he supposes, therefore, that they are brought together by their mutual attractions, and that the gradual condensation towards the centre is a proof of a central power of such a kind. He observes, also, that there are some additional circumstances in the appearance of extended clusters and nebulæ, that very much favour the idea of a power lodged in the brightest part. For although the form of them be not globular, it is plain that there is a tendency to sphericity. As the stars in the same nebulæ must be very nearly all at the same relative distances from us, and they