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.

How to divide the Circles of the Mariners Compass.

FIrst draw a Line at pleasure, and cross it in the midst with another Line at right Angles; Then in the crossing of these two Lines set one foot of your Compass, and open the other to what distance you please, and with that distance draw the Cir∣cle, which by the cross Lines of East and West, North and South, are divided into four Quadrants and equal parts, each of them containing 6 hours a piece; set VI at East and VI at West, XII at North, and XII at South, so have you the four first Divisions of your Figure: Then keeping your Compass at the same distance as you draw'd the Circle, set one foot in the crossing of the Line and the Circle at East 6, with the other make two marks, one of II, and X. Then set one Foot in the West at 6, on the other side mark out the hours of II and X, as before; keeping the Compasses still at the same distance, set one Foot at South XII, and with the other you shall mark out the Hours of VIII and IIII. Then set one Foot of your Compas∣ses at North at XII, and in the same manner mark out the Hours of VIII and IIII. Thus the Circle is divided into 12 equal parts, and each of them contains 2 hour

piece; so that it will be easie for you to divide each of these into two parts; which done, you have the 24 hours. Lastly, you may divide each hour into 4 equal parts, which will be quarters of an Houre, as you may see in the Figures.

To divide a Circle into 360 equal parts, is a thing very necessary; for in all Que∣stions in Astronomy, and in the Calculation of all Triangles, these parts are the mea∣sure of the Angles: so that in respect of this, every Arch is supposed to be divided into 360 equal parts or Degrees; and every Degree is supposed to be divided into 60 lesser parts, called Minutes. To divide a Circle after this manner, draw a Line at pleasure, and cross it at right Angles with another Line, and draw a Circle as before. Keep your Compasses at the same distance, and divide the Circle from the 4 Quar∣ters into 12 equal parts. Then closing your Compasses, divide each of these into 3; so you have in all 36 parts. Then you may easily divide with your Pen each of these parts into 10 little parts, as you may see in the middle Circle of the Figure, which are Degrees.

For the 32 Points of the Compass, draw the Line of North and South, and cross it at right Angles with the Line of East and West, and draw the Circle, as before; and with the same distance, set one Foot of your Compasses at East, and with the other draw a small Arch at A and B, and cross it from North to South with the same distance; the like do from the West Point to C and D. Then laying your Rule cross-ways to these Crosses, draw the Line BD and AC; so is your Circle divided in 8 equal parts. Then closing your Compasses, you may easily divide these 8 parts into 4; divide one, and that distance which will divide all the rest into equal parts, if you have followed Directions. And so you have the 32 Rhombs or Points of the Com∣pass; and so you may subdivide these Points into halves and quarters, as you may see in the Figure. So have you made the Mariner's Sea-Compass. The Use shall be shew'd in its place.

[illustration] diagram of a compass

The Figure of the Compass, and the Traverse Quadrat, joyned both together.

The Traverse Quadrat sheweth the making of the Traverse Table, in Chap. 3. Of Sayling by the plain Sea-Chart.