that being done, you fee where, and in what Proportion the Rumb cuts every Meridian and Parallel it meets with; then in fuch Parts or Proportion you muft make Points the Meridians and Parallels of the Globular Chart; and a Curve Line drawn through thofe Points (with a steady Hand, or a Bow) will be the Rumb required.

Thus fuppofe I would draw the N. E. by N. Rumb on the Globular Chart, in the Latitude of 20 Degrees. Firft I draw the Meridians and Parallels of Mercator's Projection, and from the Parallel of 20° I draw the ftraight Rumb Line AB, and observe it to cut the Parallels and Meridians it paffeth over in the Points a, b, c, d, e, f, g, h, i, k, l ; then I take fimilar or like Points in the Meridians and Parallels of the Globular Chart, and thro' them draw the Rumb required.

And after this Manner I have drawn all the Rumbs of the above mentioned Cafe on the Globular Chart; having alfo (for the fake of the young Learner) fubjoin'd a Scheme of their Projection on Mercator's ; fo that by comparing both in one View, the Facility and Truth of the Matter will the more evidently appear.

Note. It will be fufficient to project only one Quadrant of the Rumbs; the reft falling in the fame Manner, only in different and contrary Parts of the Chart.

The

The Ufe of the Globular Chart take briefly thus in the following Problems.

PROBLEM I.

To find the Latitude of any Place lying between two Parallels on the Chart.

Practice.

If the Place lye on any Parallel defcribed, the Latitude is known by Inspection.

But if the Place lye between two Parallels described on the Chart, as fuppofe the Point e, between the Parallel of ten and twenty Degrees latitude; then with the Compaffes take the Distance be, and fet from E on the graduated Meridian upwards, and the other Foot will fall on 17° 00' the Latitude required.

PROBLEM II.

To measure the Degrees of Longitude on any Parallel.

Practice.

This is beft done by the Sector, thus; take the Distance between two Meridians on that Parallel, and fet it parallel-wife from 10 to 10 on the Line of Numbers, then meafure the intermediate Distance required, and it will be the Answer.

Thus fuppofe I take bc on the Parallel of 10o, and apply it on the Line of Numbers, then by applying bo in the fame Manner, I find it to be 4° 17'; confequently the Point O hath 24° 17' Longitude from the first Meridian AC. And though the Parallels between two Meridians might be graduated from the Equator to the Poles, yet is it not neceffary

where

where and when a Sector may be had.

PROBLEM III.

To defcribe a Rumb required from any given Point.
Practice.

Suppofe from the Point S, I would draw the NNE Rumb; Firft, I muft confider where the fame Rumb (or its oppofite S'SW) doth crofs the fame Parallel, which I find to be at O. Secondly, I meafure the Distance SO by Prob. 2, and find it 20°. Then thirdly, I fet off 20° on every Parallel from the Interfection of the faid Rumb therewith And laftly, thro' the Points in each Parallel by this Means found, I defcribe the Curve S P, which will be every where 20° Distance from the given Rumb O R ; and it will be the NNE Rumb from the Point S as required.

PROBLEM IV.

To measure the Difference of Longitude made by a Ship's Way.

Practice.

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Suppofe a Ship at T in Latitude 25° 30' fail NE by E'till it arrive in the Parallel of 60 Latitude in V, I demand the Difference of Longitude

See where the Meridian paffing through T cuts the Parallel of 60°, which is at U; then meafure UV as directed in Prob. 2, and you will find it 71o 30', the Difference of Longitude required:"

PROBLEM V.

To measure the Distance failed on the Rumb, and alfo on the Arch of a great Circle.

VOL. II.

Tt

Practice

Practice.

This is to be done by a Scale of equal Parts or Leagues on the Chart, thus; fuppofe I would know the Distance failed from T to V, I take an 100 Leagues in my Compaffes, and run it along on the Rumb TV, and by fo doing find the faid Distance to be very near 1580 English Leagues; each of which contains 23 English Statute Miles.

The dotted Line from T to is the Arch of a great Circle paffing through both Places (as being the nearest Distance between them) which measured by the fame Scale of equal Parts will be found 1515 Leagues; which is lefs than in the Rumb by 65 Leagues, or above 1505 English Miles.

PROBLEM VI.

To measure the Meridian Distance, or Departure.
Practice.

Take an 100 Leagues in your Scale, and run it along in the Parallel of 60 from U to V, and you'll find this Parallel Distance from the Meridian or Departure to be about 920 Leagues.

Again measure the dotted Line from U to V, by the fame Scale, and you will find it to be about 850, which is 70 Leagues nearer than in the Parallel.

And these Distances being measured by a Scale of equal Parts is the greatest Excellency of this Chart. But when every thing is confidered, the Preference will always be due to Mercator's Projection.

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