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. XXXIV. How to make an effectual Shot out of a Piece of Ordnance at Random.

EVery one that hath Charge of a Gun, must at one time or other get leave of his Commanders to make two or three Shots at least out of the same Piece, and mea∣sure the Distance from the Platform to the first graze of the Shot, you must apply it to this Table by the last Rules of Proportion in the last Section, and find what deg. you shall need Mount the Gun to for any other Shot at any other time, when you shall have oc∣casion; when you have Loaden your Piece, as you are directed in Sect. 32, take the Distance to the Mark in the XVI Chap. of the second Book of the Description and Use of the Quadrant I have shewn you; and also observe how many degrees the Platform is higher or lower than your Mark by your Quadrant on the back-side of your Scale; after you have done that, then Calculate by the last Rules what degree the Gun must be Mounted to, to reach the Mark, if the said Work be under the Platform, Substract the Difference found by your Quadrant, out of the degree of the Random; but if the said Mark be higher than the Platform, Add the degr. of that Altitude to the degree of the Random, and at these corrected degrees Mount your Piece.

How to Mount your Piece by your Scalc and Quadrant thereon.

* 1.1To the side of the Scale or Quadrant is a piece of Brass fitted of the same breadth, with two Screws, and holes fitted to screw the Brass Plate two Inches of the former length, without the Edge or Side of the Line of Numbers, for to take any Angle that is under the Line of Level; for if you put the Brass into the Mouth of the Piece, the Line of Numbers being next unto it, and put in the Tompkin into the Mouth likewise to stop it fast in the middle of the Metal at the bottom, and then the standers by raise the Britch with Crows to what degree you please; and so likewise if the Mark or degr. assigned be above the Line of Level, if the Scale will not stand fast by the degree of the Diameter that fits the Bore, putting of it just into the Mouth of the Piece, then screw the Brass Plate to a hole made on purpose for the other side, and turn the degrees of the Diameter to the Bore, and fasten it with the Tompkin in the middle of the Mouth, as before; and so this Instrument will be most useful for all things as belong to a Gunner, with less trouble and Charge, than any other that ever was made by any other Men, and far more useful.

Then the Instrument being in the Mouth of the Piece, as before directed, mark di∣ligently until the Plumb-Line, which proceeds from the Centre of the Quadrant, cut these assigned degrees and Parts of degrees that you are to Mount the Gun by, in the Arch which is Divided into 90 degrees in the outward Circle thereof; your Gun so Loaded and fitted, as beforesaid, make your Shot, for without question, you will make a good Shot, and strike or came near the Mark.

As for Example.

Suppose you make tryal of your Gun as is spoken of in the last Section 32, you find that at 4 degrees of Random upon a Level-Ground the Shot is conveyed 704 Paces, if you be called out in hast upon Service against a City, or other Fort, and being ap∣pointed to play your Gun towards it, you also find it to be beyond the reach of the Right-range of your Shot, and the Distance being 560 Paces; and also that the place is lower than where you can Plant your Gun by one degree and ⅙ or 10 min. then to know the degree of Mounture, you may work as by the last Rule, if 704 gives 370 against four degrees, what will 560 give? the Distance to the Mark, it will give you the Number 295; look for this Number in the last Table 295, or the nearest Number to it, and against that degree and Part of a degree, which must also be found by Sub∣stracting the nearest less Number out of the nearest great Number, the greatest Num∣ber in the Table is 323, the nearest least is 274, the Difference is 49, the difference betwixt 323, and 395, is 28, the half of 49 is 24 ½, which shews that degree is 2 and a little above ½ of Random; but because the Mark is lower than the Platform, Sub∣stract one degree ⅙ or 10 min. out of 2 degr. 32 min. and the Remain is 1 degr. 22 min. the true height the Piece must be elevated, to reach the Mark; but if the Shot graze to the right or left, you are to mend it by direction in Sect. 31, but ever by the Example or Direction there.

Suppose the Shot graze over the Mark 20 Paces, Substract this 20 out of 560 the Distance, and Mount the next Shot according as if the Mark were but 540 Paces distant, if 20 Paces too short, make the next Shot as 580 Paces, that is the degree that is found by that Proportion to reach so far.

Notes

• * 1.1

  The use of the Quadrant on back-side of the Scale in the third Chap. for the Mounting of the Piece.