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. V. How to make the East Aequinoctial Dial, or the West Lat. 51 d. 30 m.

THis Plane is a right Horizon of those People who dwell under the Aequator, distant from us 90 deg. of Longitude; as the South Aequinoctial Plane of the last Chapter was the Horizon of those who dwell under the Aequator in the same Longitude with us: Therefore these Dials are in all Points alike, only the Substiler Line, which in the South Aequinoctial Dial is at 12, is but 6 in the morning for our Country, because of the difference of Longitude.

To pourtraict this on a Wall or Plane, first draw the Horizontal Line AB; then upon the Center C describe the Semicircle ADB, whereon lay the Latitude of the place 51 d. 30 m. from A unto D; so drawing GD continued, you shall have the Hour of 6: then with your Compasses take off your Scale 15 deg. of the Line of Chords, and turning them off 6 times, divide the Arch DF into 6 equal parts, and

draw prick'd or blind Lines to those Divisions, which would be all one as if you had done it thus. CD being equal to the Chord of 60, or Tangent of 3 hours, you shall make the Quadrant or true Square equal to the side thereof CDEF, and from the corner at E, you shall lay down both ways towards D and F the hours of 1 and 2, from whence draw Lines to the Center C: Next make choice of the length or height of your Pin or Stile, which you must lay down from C to G on the 6 hour Line, drawing from the Point G a Line perpendicular to the Line of 6, or parallel to the side CF, as GH, which cuts the former Lines in the Points IKLMH; through which Points drawing Lines parallel to the hour of 6, you shall have the morning hours from 6 to 11, and the hours before 6, from 4 in the morning, are equal as from 6 to 7 and 8.

[illustration] geometrical diagram

How to make the West Aequinoctial Dial.

THe West Aequinoctial Dial erect, serving for the afternoon, is drawn by the same Rules contrariwise like the East in all points, only it shews but the after∣noon hours, as the East shews the forenoon hours: When you have drawn on paper the East Dial, and set it by guess in its scituation, go on the West side of it, and you may see through the paper the picture by reflection of the West Dial; and so will the picture of the backside of the West shew you the true picture of the East Dial.

The way to calculate the height of the

Hours.	Ang. Po.	Tang.
deg.	min.	In.	par.
5	7	15	0	2	68
4	8	30	0	5	77
3	9	45	0	10	0
10	2	60	0	17	32
11	1	75	0	37	32
12	90	0	Infinit.

Stile, and the distance of the Hour-lines from the hour of 6, is the same as in the last Chapter of the Polar Plane: For suppose the length of the Stile to be 10 inches, then the length of the Tangent-line belonging to the first hour will be 2 inches and 68 parts of 100, as you see in this Table for the rest of the hours, which taken off a Scale of equal parts, and prick'd from the Aequinoctial from C towards F, and likewise upon the parallel DE: so you will make a Dial all one as by the former way, which is good proof, if you draw the Hour-lines through these two Points; and so of the rest.