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.

CHAP. XXXIII. How to find the Hour of the Day or Night by a Gold Ring and a Silver Drinking Bowl, or Glass, or Brass, or Iron, or Tin Vessel.

HAving a Gold Ring and a Silver Drinking Bowl, take a small Thred or Silk and measure the compass of the top of the Silver Bowl, Glass, or other Ves∣sel, which will be a convenient length for your use: Then put this Thred through the Ring, and tie the ends thereof together, taking up as little as you can with the knots. Put this Thred over your Thumb, where you feel the Pulse beat, upon the lower Joynt it may be; then stretch our your hand, and hold it so that the in∣side of your Thumb may be upward; and hold your Hand so over the Bowl, that the Ring may hang as neer the midst of the Bowl as you can guess: and you shall see that the beating of your Pulse (holding your Hand a while as still as you can) will give a motion to the Ring, causing it to swing cross the Bowl by Degrees more and more, till at last it will beat against the Sides thereof.

Now mark when it begins to strike, and tell the strokes as you would do a Clock; for it will strike what Hour of the Day or Night it is, and then leave off striking, and swinging also by degrees: Which hath been approved of by the experience and judg∣ment of many.

A Good Observation.

WE may take notice, That there is no Dial can shew the exact time, without the allowance of the Suns Semidiameter, which in a strict acceptation is true. But hereto Mr. Wells hath answered in page 85. of his Art of Shadows, where saith he, Because the Shadow of the Center is hindered by the Stile, the Shadow of the Hour-line proceeds from the Limb, which always precedeth the Center one minute of time, an∣swerable to 15 minutes the Semidiameter of the Sun: which to allow in the Height of the Stile were erroneous; but there may be allowance in the Hour-line, detracting from the true Aequinoctial Distance of every Hour or 15 degrees, 15 minutes. But I will go no further with this Subject, to put the Learners in doubt of the true Hour; for this is as neer a way which I have shewed you, as any projected upon Dial Planes. You may see a Geometrical Figure of it in my Problems of the Sphere.