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. VIII. How to divide a Particular Sea-Chart, according to Mercator and Mr. Wright's Projection.

* 1.1IF it be a Particular Chart you would make, you must first consider the two L••titudes you would make the Chart for; and out of the foregoing Table of Meridional parts, take the Numbers answering to each Latitude, and substract the lesser out of the greater, and the Remain is the Numbers which you must take for the extreme Parallel of Latitude.

Deg. Min.	Parts. Merid.	Differ.	Parts. Equal
30	13401		1975
20	13342	59	1921
10	13284	58	1863
55 00	13226	58	1805
50	13168	58	1747
40	13110	58	1689
30	13052	58	1631
20	12995	57	1573
10	12938	57	1516
54 00	12882	57	1459
50	12825	57	1402
40	12768	57	1345
30	12712	56	1288
20	12656	56	1232
10	12600	56	1176
53 00	12545	55	1120
50	12490	55	1065
40	12435	55	1010
30	12380	55	955
20	12325	55	900
10	12271	54	846
52 00	12217	54	792
50	12163	54	738
40	12109	54	684
30	12055	54	630
20	12002	53	576
10	11949	53	523
51 00	11896	53	470
50	11843	53	417
40	11790	53	364
30	11737	53	311
20	11685	52	258
10	11633	52	206
50 00	11581	52	154
50	11539	52	102
40	11479	52	51
30	11426	51

As for Example, I would make a Blank Merca∣tor's Chart from the Latitude of 49 deg. 30 min. to 55 deg. 30 min. and for 10 Degrees of Longitude.* 1.2 Look in the Table of Meridional Parts, and for the Latitude of 49 deg. 30 min. you will find the Number answer∣ing thereunto is 11426, and the Numbers for the Lati∣tude of 55 deg. 30 min. is 13401; the least substracted from the greater, the Remainer is 197:5 Equal Parts for the length of the Meridian-Line.* 1.3 Therefore first draw the Line AB, DC for the Meridian-Line, and cross it with two Perpendiculars, as BC and AD: Then di∣vide one of the Parallels of Latitude into 10 Equal parts, as AD, and subdivide each of those Degrees into 20 equal parts or Leagues that makes a Degree of Longitude and Latitude at the Aequator; and suppose each of these 20 Parts to be divided into 10 parts more, so will a Degree be divided into 200 parts: Then take with your Compasses 1975 Equal parts out of the Line AD, and lay from A to B, and from D to C, for the extreme Parallels of Latitude; and through each Degree of Longitude marked with 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, draw Meridian-lines parallel to the first Meridian: Then out of the Table of Meridional parts collect the Numbers answering to every 10 Minutes of Latitude, as in the first Column of this Table annexed,* 1.4 the second Column is the Number answering the Minutes of La∣titude in the Table of Meridional parts, which substra∣cted the lesser from the greater, the Remain is the Dif∣ference, as in the third Column 51 deg. for the Diffe∣rence of the two lowermost Numbers: Then add the Numbers together in the fourth Column in this manner; 51 for the first 10 minutes, and 52 added to it, makes 102 for 50 Minutes; and 52 added to 102, makes 154 for the Number of Equal parts you must take out of the Line AD for 30 min. from A to 50 Deg. of Latitude,* 1.5 and lay it on both sides of the Chart, and draw the Parallels of 50 Degrees of Lati∣tude; and so do of the rest, as you see in this Table. And for 51 Degrees the Number is 470; take 470 and lay it upwards from A to 51 Degrees on both sides, and draw the Parallels of 51 Degrees of Lati∣tude; and so do with all the rest.

[illustration] geometrical diagram

A Particular Sea Chart

Notes

• * 1.1

  〈 math 〉〈 math 〉
• * 1.2

  〈 math 〉〈 math 〉
• * 1.3

  Divide the Dif∣ference 197:5 by 20, the Quo∣tient will shew you the number of Degrees of the Aequinocti∣al and min. that makes the length of the Meridian Line; as for 6 deg. from A to D, will be 9 d. 55 m. of the Aequator.
• * 1.4

  You may divide every 10 Mi∣nutes into two Equal parts; so is every Degree divided into 5 min. as AB & DC into 10 m.
• * 1.5

  From D.