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.

[ II] How to find the Epact, according to the Julian, English, or Old Account, and what it proceedeth from.

THe Epact is a Number that proceedeth from the difference which is made in the space of one whole year, between the Sun and the Moon. Note, The Solar year doth contain 365 days, 5 hours, 48 minutes; and the Lunar year, allowing 12 Moons, there being 29 days, 12 h. 44 min. between Change and Change, doth con∣tain but 354 days, 8 hours, 48 min. So that there is almost 11 days difference between the Revolution of the Sun and Moon, at every years end; which difference makes the Epact. Therefore to find the Epact for any year, first you must know the Prime Number for that year, which we found before for the year 1665. to be 13. Then you must multiply this Prime Number 13. by the difference 11. and it will make 143. which divide by 30. and there re∣maineth of the Division, that cometh not into the Quotient, 23. which is the Epact for the year required.〈 math 〉〈 math 〉 So I make no Question but that you understand how to find the Prime and the Epact for any year past, present, or to come. Therefore I hold this sufficient to express so facile a thing as this is. I have told you already, That the Epact always beginneth in March; but I shall make a small Table for those that are ignorant in Arithmetick, and cannot find these two Golden Numbers, as I may call them, for 45 years to

come, where any one may find the Prime and Epact most readily in any year you shall desire.