The mariners magazine, or, Sturmy's mathematical and practical arts containing the description and use of the scale of scales, it being a mathematical ruler, that resolves most mathematical conclusions, and likewise the making and use of the crostaff, quadrant, and the quadrat, nocturnals, and other most useful instruments for all artists and navigators : the art of navigation, resolved geometrically, instrumentally, and by calculation, and by that late excellent invention of logarithms, in the three principal kinds of sailing : with new tables of the longitude and latitude of the most eminent places ... : together with a discourse of the practick part of navigation ..., a new way of surveying land ..., the art of gauging all sorts of vessels ..., the art of dialling by a gnomical scale ... : whereunto is annexed, an abridgment of the penalties and forfeitures, by acts of parliaments appointed, relating to the customs and navigation : also a compendium of fortification, both geometrically and instrumentally / by Capt. Samuel Sturmy.

CHAP. II. How to take the Plott of a Field at one Station taken in the middle thereof by the Azimuth-Compass.

BEfore you go into the Field, you must Rule a piece of Paper in 8 Columns as you see the Figure following in this Chapter, makes all plain, without any more Description, which is called a Field-Book. Secondly, when you come into the Field, first place Marks at the several Angles of the Field, as at ABCDEF, in the following Figure; then make choice of some con∣venient place about the middle thereof at 0, to fix your Compass, if you can see all the Marks; and be sure the Brass-Diameter and Slits before descriebd, be set directly over the Meridian or North and South Line of the Chard, and there fixed.

This done, direct your Sights to your first Marks at A, Marking what Degree the Index cutteth, which let be 36 Degr. 45 Min. you may estimate the Minutes; This you must note down in your Field-Book in 1 and 2 Column thereof, as you see in the Book it is plain set down; then measure the distance from 0 the place of the Compass to A your first Mark, which let contain 8 Chains, 10 Links, which must be placed in th 3 and 4 Column of your Field-Book, as you see in the Figure of the Book.

[illustration] geometrical diagram

Then direct your Sights to B the second Mark, and note the Degrees cut by the Inde•…•… which let be South Easterly 80 Degrees 45 Minutes, and the distance 8 Chains 75 Lin. You must put down in the Field-Book, as before; First, the Letter B; Secondly, the Inclination to the Meridian cut by the Index South Easterly 80 Degr. 45 Min. in the third Column; then 8 Chains 75 Links in the fourth, as you may see in the Columns in the Book, all plain; then direct your Sights to C your third Mark, and note the Degrees cut by the Index, which let be S. E. 16 degr. 45 min. and the distance OC 10 Chains 45 Links, put the same down in the Field-Book likewise, as before directed; then direct your Sights to D, and note the Degrees cut by the Index, which let be S. W. 32 degr. 00 min. the distance OD, 8 Chains 53 Links, Note it down in the Book, as before.

Then direct your Sights to E, the Index cutting 72 degr. 45 min. North Westerly; and the distance OE 8 Chains 15 Links: They must be noted in the Book as the rest are.

Lastly, direct your Sights to F your last Mark, the Edge of the Index cutting in the upper Brass Circle N. W. 18 degr. 00 min. the distance OF 9 Chains 55 Links; then will the Observation stand in the Field-Book as in the following Table or Figure; then by a line of Chords, or by the Protractor you may presently Protract the exact Figure of the Field upon Paper thus, By a line of Chords; take 60 degr. and draw the Circle. Secondly, draw the Meridian line of North and South, and parallel-line of East and West. Thirdly, your first Observation and degr. cut by the Index, was 36 degr. 45 min. N. E. Therefore take 36 degr. 45 min. off the line of Chords, and lay from the Meridian line M to N. Fourthly, the distance OA was found 8 Chains 10 Links; take with your Compasses off any Scale of equal parts, 8 Chains and 1/10 that stands for 8 Chains 10 Links; lay this distance from O to A, and draw the prick'd line OA.

Then secondly, take out of the line of Chords the second Angle S. E. 80 degr. 45 min. and lay from the South towards the East on the blind-Arch, and through it draw the line OB; then take off the same Scale of equal parts 8 Chains 75 Links, that is, 8 parts, and 75 parts of 1 divided into 100, and lay it from O to B, and prick the line from O to B, and draw the line AB, which measure with your Compasses, and apply it to the Scale of equal parts as before, and you will find the side AB 8 Chains 75 Lin. The like do by all the other Angles and distances in the same manner as you have been shewed in the two first Angles. The Figure makes it so plain, it need no further precept; and you may put down the Number in the side, as I have done.

Now by the Protractor in the Second Book described.

* 1.1You may lay the Diameter-Edge thereof on the North and South line, and through the Center, put a Pin on the Center of the Plott at O, and note the degr. and distances in the Field-Book, as before: the first was North Easterly 36 deg. 45 min. put the Edge of the Index to 36 degr. 45 min. in the Arch of the Protractor; and by the Edge account in the Scale thereof 8 Chains 10 Links; and by the side thereof draw the line AO, prick'd as before; and so do by the rest of the Angles and sides in like manner, and you may presently draw a Plott of Ground you have measured. This is very plain, and may be understood by the meanest capacity in this Art. The Observations Marked in the Field-Book stand as in the following Table.

The manner how the Field-Book must be Ruled.

Mark.		D. M.	Ch.	Lin.
A	N. E.	36 45	08	10
B	S. E.	80 45	8	75
C	S. E.	16 45	10	45
D	S. W.	32 00	8	53
E	N. W.	72 45	8	15
F	N. W.	18 00	9	55

You are to note, that every Degree in the uppermost Brass-Circle is supposed to be divided into 60 parts, which is called Minutes, which cannot be expressed in regard of the smalness of the Instrument or Circle of Brass on the Glass of the Compass; and therefore the odd minutes must only be estimated: so must the odd Links taken off your Scale of equal parts, and it will breed no sensible Errour.

Notes

• * 1.1

  Turn the Pro∣tractor after you have laid down all the Angles in the NE. and S. E. quarterly, and lay the Center-Pin of the Pro∣tractor on the Point O, as be∣fore; and the Diameter on the Meridian-line••