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.

SECT. V. The Ʋse of the Quadrant and Variation-Compass in the First Book, on the Instrument of the Moon for shifting of Tydes.

This Instrument contains two Parts or Rundles, which are the two uppermost in the aforesaid Instrument made of Wood or Brass, moving one upon the other, as there you may see. The biggest of the two uppermost Rundles represents the Compass you Steer the Ship by, which is subject to Variation: but the upper Compass doth repre∣sent the true Compass that never varieth, whereby you have a most necessary Instru∣ment to rectifie the Compass, as Mr. Wakely hath made Tables to be used with it; but this will serve for use as near by the Quadrant.

Admit I am in the Latitude of 27 Deg. and Declination 20 Deg. Northward, and I observe the Sun's Rising and Setting to be due East and by North, and West by South Point of my Steering or Variation-Compass; the Variation in that Latitude is required.

The Sun having North-Declination, and in that Latitude of 27 Deg. if there be no Variation the Sun will rise (as you may presently find his Amplitude by the Qua∣drant and Index, 22 Deg. 34 Min. which is but 4 Min. not to be taken notice of,* 1.1 above) E. N. E. and sets W. N. W. But according to the foregoing Propositions, the Sun did rise at E. b. N. and set at W. b. N. Therefore it plainly appeareth that there is a full Point Variation.

Therefore on the Variation-Compass on the Instrument of the Moon, you must al∣ways bring the true Point of Rising and Setting on the upper Compass, to touch the false Point or Rising and Setting, found by Observation and Steering-Compass, on the

middle Rundle, being set in this Position. You will find the E. b. N. to be the true E. N. E. and the W. and by N. to be the true W. N. W. and the N. b. E. to be the true N. and the S. b. E. to be the true S. and the S. E. ½ Point Southerly, to be the true S. E. b. S. ½ Southerly; and the South 3.1/4 East, to be the South ¼ West: And so you may do with ease in all other Observations, in like manner as you have been shewn, by Points, Halfs, and Quarters, which is on the two Trundles; and be sure nearer than ¼ of a Point I never did see any man Steer or sheape a Course.

Notes

• * 1.1

  11 d. 15. to each Point.