Tycho fix it at Uranoburg, an Island in the Danish Streights, and calculate the celeftial Motions to that Place, and from thence accommodate them to the reft. Others chufe other Places according to the Authors of the Ephemeris they use, who calculate the Ephemeris, and the Planets Places for the Meridian of their own Place. As Origanus for Frankfort; Maginus for Venice; Eickftadius for Stetin; Lanfberg in his Tables takes Gafa in Zeeland, and Reinholdus the Royal Mountain of Pruffia.

BUT to say the Truth, all this Difference hath arifen without any Foundation; fo that they are to be blamed who first changed Ptolemy's Meridian: for it is no matter where they begin, whether at a Place remarkable, or moft to the Weft or Eaft, provided we may know the Situation and Distance of other Places from it accurately; and that variety of firft Meridians hath burthened the reading of Geographical Writers with Confufion and Difficulty. Yet because the Knowledge of the Variation of the Needle from the Meridian is of great Advantage, and that Variation encreases to a certain Meridian, and then decreaseth; it will be useful for finding that Variation, and comparing the Increase and Decrease of it, to chufe that for the firft Meridian, in which, or in moft Places of it, the Needle hath little or no Variation; if any fuch is to be found.

AND feeing the Dutch now use that which goes over Teneriff, and they fail to all Parts of the Earth; it will be convenient to ufe that with them, for the better understanding the Diaries they publish...

AND Students fhould know in reading of Au thors, that where mention is made of the Longi VOL. II. Lin

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tude of a Place, or of a certain Meridian, where the Author begins his firft Meridian.

PROPOSITION III

Having the Latitude and Longitude of a Place, to find it on the Globe or Map; and fo it's Situation and Distance from other Places.

THE Problem for which a Method is fought with fo much Care and Industry, is, to find the Longitude of the Place in which we are; and before I come to it, I thought fit to premise the Pro blem for which the Longitude is wanted; left the Reader fhould be difgufted for want of knowing the ufe whereto it is fubfervient.

FOR Seamen (as to those that travel by Land they have not much need of it) having gone far from Land, and not being fure of the Way they went, because of feveral Difficulties, they cannot trace it out certainly in the Maps, and fo cannot determine the Ship's Place, or the Course they muft fteer to their defired Port; which they could do if they had both their Latitude and Longitude. Mathematicians have taught them to find the Latitude at Night by the Stars, and in the Day by the Sun; as we have fhewn before: they that pretend to do it by the Magnetic Needle, fhow their want of Skill. And if they had the Longitude, then where the Meridian they are in cuts the Parallel of their Latitude is the Place they are in, on the Globe or Map. And this Method of the Section of two Lines is ufed frequently to find a Point's Place.

FOR the Solution of the third Problem, count the Degrees of Latitude from the Equator on the brafs Meridian, and having chalked it, draw the Parallel; then bring the known Meridian the Place

is in (which is diftant from the first by the Dea grees of Longitude) under the brafs Meridian, and where it cuts the Parallel of Latitude is the Place fought: if any Meridian be drawn thro' the Place, the Work is easier.

IN ftrait lined Maps (fuch as the Seamen's are) find the Latitude on the Margins on both Sides, and draw a Line thro' them which represents an Arc of the Parallels; then at the Head and Top find the Longitude, and draw a Meridian thro' the Degree of Longitude, the Point of Interfection is the Place. Or fhorter thus; Lay a Ruler on the Degrees of Longitude, at the Head and Bottom, and fet the Degree of Latitude taken from the Map with a Pair of Compaffes along the Side of the Ruler, and you have the Foint. And the fame Way in curve lined Maps; only we muft draw circular Parallels.

THIS is the first remarkable Ufe of the Longitude in failing.

THE fecond ufe is more neceffary; viz. the Conftruction of Globes and Maps thereby; for the Places are by the Latitude and Longitude fet down on Globes and Maps: and hence it is they are often made fo as not to reprefent the Situátion of the Place truly, for want of the true Longitude.

THE third ufe is alfo famous; viz. the knowing the Hour in other Places when any celeftial Appearance happens; of which in the following Propofition.

THE fourth ufe is to find the Distance of two Places; having their Latitude and Longitude given.

PROPOSITION IV.

The Sun, Stars, and every Point of the Equator or Parallel removes from the Meridian 'tis in, fifteen Degrees in an Hour, or in a Minute of Time, fifteen Minutes of a Degree; and in four Minutes one Degree.

FOR an Hour is but the twenty fourth Part of time in which they revolve from any Meridian 'till they return to it; and three hundred and fixty Degrees in the Circle divided by twenty four gives fifteen in the Quotient.

THE fame will appear on the Globe: bring a Point on the Equator to the Meridian, and the Index to 12, turn the Globe 'till the Index Point to 1 or 2, and you will fee fifteen Degrees have paffed thro' by the Meridian.

COROLLARY.

IF a Place be fifteen Degrees more eafterly than another, it will be eight or nine o'Clock with them by an Hour fooner than in the other Place; if thirty Degrees, two Hours fooner; and fo they will have the heavenly Appearances fo much fooner than the other: but if more wefterly than the other, they will be fo long behind the other in their reckoning: or, which is the fame thing, if one hath an Appearance in the Heavens, as an Eclipfe, an Hour fooner than the other, they will be fifteen Degrees more easterly.

Note. When we add the Sun and Planets with the fixed Stars; as in faying they move fifteen Degrees wefterly each Hour; we do not understand it to be exactly fo, for tho' it is true of the Stars, yet because the Sun and Planets in the mean time revolve

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revolve to the East, they come later to the Meridian, and by degrees they remove from the fixed Stars; but it is fo little in a Day, (being in the Sun but ten Seconds, and in the fuperior Planets lefs), that they are accounted to move fifteen Degrees in an Hour, as the fixed Stars do.

PROPOSITION V.

Having the Time of an Appearance in the Heavens with us, and with others, to find the Difference of their Longitude from ours.

THS is easy from what hath been faid. You are only to turn the Difference of Time into Degrees; counting fifteen Degrees for an Hour: and if their Hours be lefs than ours, then they are to the Weft of us, but if more, to the Eaft.

PROPOSITION VI.

Having again the two Times in which there is any remarkable Appearance in the Heavens; to find the Difference of Longitude by the Globe or Map.

TURN the Difference of Time into Degrees, as before; and bring the one Place to the brafs Meridian; and confider whether the other lies to the East or Weft of you, by their Hours being more or fewer, as before; if to the Eaft, count fo many Degrees on the Equator easterly, and turn the Globe so many to the Weft, and the Meridian under the brass Meridian fhows the Longitude of the other Place. This may be done better by the Index of the Hour Circle, as before. And on the Map, apply a Ruler to the Longitude of the one, and count fo many Degrees on the Map to the other.

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