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. XII. How to know what Diameter every Shot must be of to fit any Piece of Ord∣nance, or to choose Shot for Ordnance.

TAke the Diameter of the Bore of the Piece, and Divide into 20 equal parts, and one of those parts is sufficient vent for any Piece, the rest of the 19 parts must be the height of the Shot; but now adays most Gunners allow the Shot to be just one quarter of an Inch lower than the Bore; which Rule makes the Shot too big for a Cano••, and too little for a Faulcon; but if the mouth of the Piece be grown wider, then the rest of the Cylinder within by often shooting; to fit Shot to such a Piece, you must trie with several Rammers-heads, until you find the Diameter of the Bore in that place where the Shot useth to lie in the Piece; and a Shot of one twentieth part lower than that Piece is sufficient; therefore let Gunners remember to trie the Piece, as di∣rected.