Draw a line to represent the meridian of Greenwich, from which fet off towards the left hand 25 degrees of weft longitude, as before directed; through the two laft points draw lines parallel to the meridian of London, and thefe will be the extreme meridians, or eaft and weft bounds of your chart.

Having drawn the two meridians on the lower edge of the paper, draw a line perpendicular to the meridians, to represent the parallel of 14 degrees north; then, from the meridional parts answering to 15 degrees 910, fubtract the meridional parts answering to 14 degrees 849, and take the difference, 61, in your compaffes, and fet it off from the parallel on both the meridians from you, and that will represent the parallel of 15 degrees.

Again, take the meridional parts of 15 degrees 910, from the meridional parts of 16 degrees 973, and fet off the difference 63, upon the meridians from the point reprefenting the parallel of 15 degrees, and that will reprefent the parallel of 16 degrees. In like manner proceed to set off the parallels upon the meridians.

Or, if the meridional parts of 14 degrees be fubtracted from the meridional parts of every fucceeding parallel, and the difference be fet off from the parallel of 14 degrees upon the meridians, thefe points will represent the feveral enlarged parallels of latitude, the fame as before; and, if it be required that the meridians fhould be divided into degrees and minutes, the meridional parts for fuch must be taken from the Table, and set off as above.

Having fet off as many parallels as you intend the chart should contain, through each point draw parallels; or if you think drawing lines through every degree will crowd your chart too much, you may divide the borders only into fingle degrees, &c. and draw lines through every 5 degrees of latitude and longitude, as in the

chart.

Take from the Table of Latitude and Longitude of Places, the latitude and longitude of each particular place contained within the bounds of the chart, and lay a ruler over its latitude, and another croffing that over its longitude; the points where thefe crofs will represent the propofed place upon the chart. In like manner may any place be readily marked. Hence the particular points of a feacoaft may be laid down as above, and lines properly drawn from point to point will form the outlines of the fea-coasts, islands, &c. to which may be annexed, the depths of water, feiting of currents, and whatever else may be thought convenient for the chart to contain.

This map or chart is not to be confidered as a juft or fimilar reprefentation of the earth's furface, for in it the figures of iflands and countries are distorted near the poles. For

Suppose an island in the latitude 60° N. or S. where the breadth of a degree of longitude is just half as large as a degree upon the equator. Now, as the degrees of latitude are enlarged in proportion as the degrees of longitude are expanded towards the poles, it is plain, that every point of that island or country, being laid down

in its proper latitude and longitude, will be represented twice as large as it really is.

Hence it follows, that as the degrees of latitude are every where increased, like thofe of longitude, it is plain the bearing between places will be the fame on this chart as on the globe; and the proportions between the latitude and longitude and nautical diftances, will be the fame upon this chart as upon the globe.

And fince the meridians in this projection are right lines, it follows, that the rhumbs, which form equal angles with the meridians, will be ftraight lines, which render this projection of the earth's furface much more eafy and proper for the mariner's use than any other.

Gunter's Scales have drawn upon them two lines, one marked N M, fignifying the Nautical Meridian; and the other, directly under it, marked E P, fignifying Equal Parts, or degrees of longitude upon a Mercator's Chart.

Thofe are equal parts, or degrees of longitude, to which the degrees of the nautical meridian are fitted, by increafing them, in their true proportion; hence the limits or bounds of a Mercator's Chart by these lines are easily made, by transferring the divifions correfponding to the degrees to be ufed from the feale to the paper the chart is to be drawn upon: but as the degrees drawn by these lines are too fmall for the feaman's ufe, it is much better to use a fcale of equal parts as before, and, confequently, the degrees may be made of any propofed length.

By the Latitude and Longitude in, to prick off the Ship on the Chart.

RULE. Lay the ruler across the chart in the latitude your ship is in, then look upon the equator, or line marked with the degrees of longitude, for the longitude your fhip is in by your reckoning, and fetting one foot of your compaffes in that longitude, take the nearest distance to fome north and fouth line, and from where that line croffes the edge of the ruler that lies in the given latitude, lay off that same distance along the edge in the ruler to the right hand, if the longitude you are in was to the right hand of the north and fouth line; or to the left hand, if it was to the left hand; where this falls will be the place of the hip; but this will only do when the longitude marked on the chart, and your reckoning of longitude in, are both counted from the fame meridian. Therefore, for a general rule, take the following, viz.

By the Latitude in and Longitude made, to prick off the Ship's Place.

RULE. Set one foot of your compaffes in the place you take your departure from, and take the nearest distance to fome north or fouth line, and from where that falls upon the equator, or the Jine marked with the degrees of longitude, fet off that distance the fame way the place lies from it; that is, to the right hand, if the

place lies to the right hand of the north and fouth line, or to the left hand if it lies to the weft; and make a mark with a black lead pencil; this mark will ferve to prick off by, till you come to take a new departure; and then rub it out, and make a new one as before.

Then lay a ruler across the chart in the latitude you are in, and taking fo many degrees in your compaffes from the line of longitude, as your longitude made comes to, fet them off from your black-lead mark along the edge of the ruler to the eastward; if the longitude made be eaft, or to the weftward if it be weft; where this falls will be the longitude the fhip is in by the chart; from which take the nearest distance to fome north and fouth line, and from where that line, &c. as in the first cafe.

The fhip's place on the chart being found, as before taught, it remains in the next to fhew how to find the bearing and diftance of any place from the fhip; and firft,

To find how any Place bears from the Ship.

RULE. Lay a ruler from the place of the ship to the place you would know the bearing of; then fet one foot of your compaffes in the centre of fome compass near the ruler, and take the nearest distance to the edge of the ruler: then run one foot of your compaffes along by the edge of the ruler, and observe what point of the compass the other comes nearest to, which will be the bearing required.

CASE I.

To find the Distance of any Place from the Ship.

If the place be in the fame longitude that the fhip is in; that is, if it bears due north or fouth, then the difference of latitude between them, turned into miles or leagues, will be the diftance.

CASE II.

If the place be in the fame latitude the fhip is in; that is, if it bears due eaft or due weft, then take haif the diftance between the fhip and the place in your compaffes; and, fetting one foot on the line marked with the degrees of latitude, in the latitude the fhip is in, fee what latitudes the other foot will reach to, both above and below it; the difference between these two latitudes will be the distance required.

CASE III.

When they are neither in the fame Latitude nor in the fame Longitude with the Ship.

RULE. Take the difference of latitude between both places in your compasses from the equator, or graduated parallel; and laying a ruler over both places, put one foot upon the fhip's place, and

fide your compaffes along the edge of the ruler (holding both points parallel to the meridian) until the other cuts the parallel of latitude paffing through the place (or any E. and W. line cut by the ruler) then ftay the compaffes. Take the distance between where the point refted by the edge of the ruler and the place (or where the ruter crofled the aforefaid eaft and weft line) in your compaffes, and apply it to the equator, or graduated parallel, and that will give their diftance in degrees, which may be turned into miles or leagues; and in the fame manner as you find the bearing and diftance between the ship and any place, you may also find the bearing and diftance of one place from another; or if the distance between the fhip and place be taken in your compaffes, and applied to the fide of the chart, or graduated meridian, nearly in the parallels of the fhip and place, it will give the distance in degrees as before; and for this purpofe there are generally marked on the fides of charts fcales of leagues, by which the distance between the places may be readily found.

Or the distance between two places upon a Mercator's Chart may be easily found, thus:

Take half the distance between any two places, and with one foot of the compaffes in the middle parallel, extend both ways upon the graduated meridian; count the number of degrees between both points, which will be your distance, either in leagues or miles, according as the fcale is divided; or take the diftanee in your compaffes, and fet one foot as much above the one place as the other point is below the other place, on the meridian: the number of degrees between the points of the compaffes will be the distance.

EXAMPLE.

Required the Bearing and Distance between Cape St. Vincent and Teneriffe?

Lay a ruler over both places, and take their difference of latitude 8°30', from the equator or graduated parallel, in your compaffes; and slide one foot along the edge of the ruler from Teneriffe, holding the other point in the direction of the line CB, until the other point juft touches the eaft and weft line, (AB) paffing through St. Vincent, as at B, from C, where the foot of the compaffes refted, by the edge of the ruler, and St. Vincent being measured, and applied to the graduated parallel, gives 10 two-third degrees, or 640 miles the diftance.

Again, take the nearest distance between the centre of the compafs in your compaffes, and fliding them along the edge of the ruler, as before directed, you will find the course to be S. W. by S. ‡ W, nearly.

Hence the direct courfe between Cape St. Vincent and Teneriffe is S. W. by S. W. distance 640 miles, or 213 one-third leagues; and the fame with other places.

OF WINDS.

THE earth is endued with a wonderful principle of gravitation, whereby all its parts are ftrictly united together; and all bodies that are loose upon it closely adhere to its furface, tending directly towards its centre. Hence it is, that fhips are able to fail with the fame facility every where (void of impediments) upon the surface of the fea, quite round the terraqueous globe; and that (as to fenfe) there is no fuch thing as an upper or lower part of the earth; for let the inhabitant be in what part foever, he will there gravitate towards the earth's centre, and imagine himself to be on the highest point of its furface; from whence he will obferve the heavens like a large vault over his head, and his antipodes he will imagine to be directly under him, as they will alfo theirs, for the like reafons. According to this law of gravity, if the earth was at reft, (and not acted upon by any other power) and its parts loofe, or its furface all over covered with a deep fluid, it would naturally form itself into a true fphere, or globe.

Notwithstanding this power of attraction, yet the fun, whose rays upon the earth cause vapours or fumes to be continually rifing from it, which must partake of the quality of those parts from whence they are evaporated; a collection of which form what we call our air or atmosphere, furrounding the earth, and extending fome miles above its furface, and is liable to be put in motion by various causes. Hence, air is a fine elaftic fluid, and is found capable of being compressed or condensed by cold, and expanded or rarefied by heat.

Confequently, an alteration of heat or cold happening in any part of the atmosphere, the air in that part will be either condenfed or rarefied, and the neighbouring parts will thereby be put into motion, through the endeavour which the air by its elasticity or fpringiness always makes to reftore itself to its former ftate, or come to an equilibrium.

Wind is a stream or current of air, which generally blows from one part of the horizon to its opposite.

The following obfervations have been made on it, particularly by Dr. Halley, which are not unworthy the Seaman's notice. Between 30 degrees north latitude, and 30 fouth latitude, there is a conftant eaft wind throughout the year, blowing on the Atlantic and Pacific oceans, and this is called the Trade Winds.

For as the fun, in moving from east to west, heats the air more immediately under him, and thereby expands it; the air to the eastward is conftantly rufhing towards the weft to reftore the equilibrium or natural ftate of the atmosphere, which occafions a perpetual east wind in those limits.

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