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.

PROPOSITION VII. The Moon being 16 days old, I demand, What a Clock it will be Full-Sea at Bristol, Start-point, Waterford, where an East-by-South Moon on the Change-day makes the Full-Sea?

You are to consider the Point of the Compass the Moon is upon in these Ports, when it is Full-Sea on the Change-day (as in all other Ports) which in these Ports is found by observation to be always East-by-South Moon (which is 6 hours 45 mi∣nutes) Then consider whether it be the Day or the Night-Tyde you would know the Time of Full-Sea; if it be the Morning-Tyde, bring the Index of the Moon to the West-by-North Point, staying it there; bring the 16th. day of her Age under the Index of the Moon, and the Index of the Sun will point you to 7 of the Clock and 33 Minutes, the time of Full-Sea in the Morning. If it be the Evening Tyde, bring the Index of Luna to the East-by-South, and stay it there, until you have brought 16 Days and half under the Index of Luna, and the Index of Sol will point directly upon 8 of the Clock at Night, the time of Full-Sea in the aforesaid Ports: Thus you see there is 27 Minutes difference in every Tyde in these Ports. So you may know in every other Port in the same manner, if you do as before-directed, and allowing half a day more for the Night-Tyde, by turning of it half a day further. And take this for a Rule, That the Moon betwixt Change and Full is ever to the Eastward of the Sun, and riseth by day, still separating it self from the Sun until she be at the Full: Then after the Full, in regard she hath gone more Degrees in her separation than is contained in a Semicircle, she is gotten to the Westward of the Sun (rising by night) and applieth towards the Sun again until the Change-day, which you may see plain∣ly demonstrated by the Instrument.