Speculum nauticum a looking glasse for sea-men : wherein they may behold a small instrument called the plain scale whereby all questions nautical and propositions astronomical are very easily and demonstratively wrought ... / by Iohn Aspley.

CHAP. IV.

Two Ships departing from one Parallell, and Port, the one in saying eight Leagues betwixt the North, and the West, hath raised the Pole two degrees, the other in suiling a hundred Leagues betwixt the North, and West, hath raised the Pole foure degrees, I de∣mand by what Rhombes the said Ships have saild, and the Rhombe, and distance that is betwixt them.

IN the fourth Demonstration, draw the Quadrant ABC DE, then in regard the first Shippe hath raised the Pole two degrees, which is forty leagues, take forty leagues of your Scale, and apply them unto the Meridian line AG L, from A, unto G, then from the point G, draw the line GF, parallell unto AB, then opening your com∣passes unto 80 Leagues set one foot in the Centre A,

with the other, make a marke in the line GF, which will bee at F, so shall F, bee the place of the first shippe: the second shippe hath raised the Pole foure degrees, which is eighty Leagues, therefore place eightie Leagues upon the Meridian line AGL, from A, unto L, and from the point L, draw the line LM, parallell unto GHF, then open your Compasses unto the distance of a hundred Leagues, which are the Leagues the second shippe did runne, and set the foot of your Compasses in the Centre A, and with the other make a marke in the line LM, which will be at M, then draw the line MA, which is the course of the second Ship, and the line FA, is the course of the first shippe, then from F, let a Perpendicular fall, being Perpendicular to the line GF, which is the line FK, then opening your Compasses unto the Ra∣dius of your Scale, set one foot in the Centre F, and with the other draw the Quadrant HIK, likewise from F, the place of the first ship, draw a line by the point M, the place of the second ship: cutting the quadrāt KHI, in I, so let IK, be the course that is be∣twixt them, that is, if you will saile from the first ship unto the second, you must saile North, and by East, and 41 minutes to the Eastward, likewise let FM, be the distance that is betwixt them, which in this Demon∣stration is 40 Leagues, two miles, so shall BC, be the course of the first shippe from the West Northward, which here is found to be 30 degrees and one minute frō the West Northward, or Northwest, by West & 3 deg. and 44 min. to the Westward. Lastly, the Arch E D, is in the distance of the course that the second ship made from the North Westward, which is found by this Demonstration to be Northwest, and by North, and three degrees five minutes to the Westward.