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.

Rules for Observation in South Latitude.

SUppose I at Sea in a Ship the second of June, Anno 1666. and I find the Sun's Meridian Altitude by Observation to be 64 deg. 45 min. The Latitude the Ship is in, is required.

	deg.	min.
The Meridian Altitude North	64	45
The Declination North, add	23	15
The Complement of the Latitude	88	00
	90	00
The Latitude the Ship is in-	02	00 South.

Suppose a Ship at Sea the 28th of December, Anno 1695. and in Longitude 169 deg. East, and I find the Meridian Altitude by Observation to be 59 deg. 52 min. The Latitude the Ship is in, is required. The Declination in the Meridian of Bristol for the 28th of December, is 22 deg. 25 min. and the daily difference of Declination is at this time 8 min. Therefore if you look in the Table of Proportion following, you will find the Proportional Minutes to be about 4, which you must add to the Declination of the Meridian of Bristol, and the Sum will be the true Declination for the Longitude 169 deg. East, which is 22 deg. 29 min.

	deg.	min.
The Meridian Altitude North	59	52
The Declination South, substr.	22	29
The Complement of the Latitude	37	23
	90	00
The Latitude the Ship is in, which was	52	37 required.

Suppose I were at Sea in a Ship the 29th of June, 1679. and I find the Sun's Me∣ridian Altitude to be 62 deg. 30 min. North, The Latitude is required.

	deg.	min.
The Meridian Altitude North	62	23
The Declination North, add	22	26
The Complement of the Latitude	84	49
	90	00
The Latitude the Ship is in	05	11 South.

Admit I am in a Ship at Sea the 20th of January 1667. the Sun's Declination 20 deg. 4 min. and the Sun's Meridian-Altitude 79 deg. 36 min. South, I require the Latitude the Ship is in.

Answer, 9 deg. 30 min. South.

Admit a Ship were at Sea, the Sun's Declination 13 deg. 53 min. South, and the Sun's Meridian Altitude 80 deg. 43 min. South, The Latitude is required.

	deg.	min.
The Declination South	13	53
The Meridian Altitude	80	43 add.
	94	36 the Sum.
Substr.	90	00
The Latitude the Ship is in	04	36 South.

If you observe the upper part of the Sun, you must substract 16 min. But to the contrary, if you observe the lower part of the Sun, you must add 16 min. for the Sun's Diameter, and the Sum will be the true Altitude of the Sun's Center.