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.

2 Example.

But suppose the Magnetical Azimuth by the Needle had been	37 d. 03′
And the Suns Azimuth found, as before, to be	48-18
Substract the lesser out of the greater, the difference NE	11 d. 15

And in regard the Magnetical Azimuth is less than the true Azimuth by 11 deg. 15 min. therefore the difference and variation is Easterly one Point, which is 11 deg. 15 min. and consequently all the Points, stand 11 deg. 15 min. or one Point to the left hand out of their true Places; and therefore, to make good a North Course, you must Sail by your Compass N by E; and an East Course, Sail E by South, and South Sail S by W; and to make good a West Course, Sail W by N; and so it is to be understood of all other Courses or Points; for in this Example, the true Course makes an Angle with the Meridian of 48 deg. 18 min.

The Year 1666 at Bristol, in Rownam Meadows, My self and Mr. Phillip Stainard, and some other friends Masters of Ships, took with us a Quadrant described in the 16 Chapter of the Second Book of 20 Inches Semi-diameter, and one Needle, and one A∣zimuth Compass, described in the First of the Fifth Book, the Needle about 9 Inches long, the Chard 8 Inches; and in the Afternoon we made these Observations follow∣ing.

Declin. 23 d. 30′ dist.	66 d. 30
Altitude 44:20 Com.	45:40	As the Radius is in proportion—10
Latit. 51 d. 28 m. Com.	38:32	To the Co-Sign of the Latit. 38 d. 32′ 970446
The Sum	150 42	So is the Co-Sign of the Alt. 45 d. 40 985447
The half Sum	75 21	To the fourth Sign 26 d. 27 m. — 964287
The difference	8:51

Add the Radius to the Sum; Take the half is the Sign of half the Ark.	As the fourth Sign 26 degr. 27 min.	964893
is to the Sign of the half Sum 75 d. 21′	998564
So is the Sign of the difference 8 deg. 51′	918709 add
	1917273 sum
	to the seventh Sign 19 deg. 31 min. (add Rad.)	1952380
the half is the Mean proportional Sign of	35:19976190

☉ Obser. Altitude.	Magnetical Azimuth.	Suns true Azimuth.	Variation VVesterly.
Gr. M.	Gr. M.	Gr. M.	Gr. M.
44 20	72 00	70 38	01 22
39 30	80 00	78 24	01 36
31 50	90 00	88 26	1 34
37 42	95 00	93 36	1 24
23 20	103 00	101 23	1 23

Which doubled, is 70 deg. 38 min. the Suns Azimuth from the South part of the Meridian, or 54 degr. 41 min. the Complement of 35 deg. 19 min. doubled, is 109 deg. 22 min. the Suns Azimuth from the North part of the Meridian; and so of the rest, as they are set down in this Table, viz. from the South part of the Meridian.