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. XXXI. The difference of Shooting by the Metal, and by a Dispert by a Right Range, and at Random, by the Figures following.

SHooting by the Metal* 1.1 is the Figure AB, that is, admit you raised the Muzzle-ring, and the Base-ring, and the Mark, and your Eye in a Right-line, if you put the Scale into the Muzzle with the Plummet hanging to it, you shall find it differ 4 or 5 or 6 degr. according to the length or Mark of the Piece, and in regard of the several diffe∣rences of the length and marks, or Diameter of her Base and Muzzle-ring, no certain proportion can be generally assigned; yet for most Pieces it hath been well observed, that the Piece directed by her Metal, will shoot about twice as far as when the Mark is level and set by a Dispert & Quadrant and the Sight-line parallel to the Horizon; so that admit a Piece were laid by the Metal of Base and Muzzle-ring, and that it differed from a right Level 6 degr. as you found by your Quadrant in the Scale, you fired at the Mark, the Gun so layed, and measuring the distance you find it 412 Paces, which is as much beyond the Mark, as it is to it, which is the difference of Shooting by the Dispert* 1.2 or Axis of the bore in right bored Pieces following, this is chlled Point-blank; for if you acknow∣ledge the higher the Muzzle of a Piece is elevated, the farther the Shot is carryed in a Right-line. There can be no Point-blank directly known, nor Rules to know them, without you take a Piece and make 11 Shots out of her, and so by it proportion a Table, as here is one following. You must have leave, if possible, to Shoot so many Shots in a Piece at such elevations with the like goodness and quantity of Powder, as will make you such a Table of the Proportions of Right Ranges, called Point-blanks, before you can have any guess certainly of Proportion for other Guns; but to make a good Shot at a Mark, first be sure your Guns Trunnions be placed right, the Carriage well made, the

Platform clean swept, and that the ground be Level, and that the Carriage-Wheels be one as high as the other, and whether the Axle-tree be placed just across the Carriage, or not; or whether the Piece be true bored or not, if it be a true bored Piece, set your Dispert on the Muzzle-ring, just over then Centre of the Muzzle of the Piece, which may be done by holding a Line right before the Muzzle, and two Sticks or Notches made in Sticks put on the Muzzle-ring, and by the Line you may easily find the middle where to put the Dispert; and likewise if the Line touch the upper side & lower side of the Metal alike, you may be sure the Gun lies Level, or by the Scale and Quadrant on it and Plumb-line, if it hang in the Mouth of the piece, and no degrees of Altitude, but by the Long Side-line thereof, be sure the Piece is Level, and will carry the Bullet Horizontally in his violent Course; therefore by your Crows and Standers by, or Matrosses set about the Piece to the Mark, as at D, that with your Eye two foot from the Base-ring you may see the Mark on the upper part of the Base-ring, the top of the Dispert, and the Mark or Turret you Shoot at in a Right-line, as CD, and this you may call Point-blank, and all Shooting in this Form, and no other.

A Table of Point-blanks.

d••g.	randoms
0	192
1	209
2	227
3	244
4	261
5	278
6	285
7	302
8	320
9	337
10	354
20	454
30	693
40	855
50	1000

On the upper part of the Base-Ring, the top of the Dispert, and the Mark or Turret you Shoot at in a Right-line, as CD; and this you may call Point-blank, and all Shooting in this form, and no other.* 1.3

But for Shooting in a Right-line called the Right Range of a Bullet out of any Piece for making of Batteries, or Shooting at Random at any advantage, you may make use of this Table, until by your own experience, you have made out of a Gun by Shooting first Level, and afterward from degree to degree to 10 degrees mounture, or more in a Right-line.

The use of the Table of Right-Ranges, or Point-blanks before-going, it is found by experience, that the Piece assigned at six degrees of mounture Shoot 200 Paces in a right or insensible crooked Line; I desire to know how far the same Piece will Shoot in a straight Line, being mounted to 10 degrees? say by the Table if 285 the Number against 6 degrees giveth 200 paces, what will 354 the Number against 10 degrees give? I answer, 248 4/10 paces.

The Logarithm of 6 degr. is 285.	245484* 1.4
The Logarithm of the Paces known 200	230103
The Paces against 10 degr. is 354 is	254900
The Sum	485030
give the Logarithm of 248 4/10 Paces	239519

Or extend the Compasses from 285 to 200, the same distance will reach from 354 to 248 4/10 Paces as before 200 × 354/285 = 248 4/10 Paces, as before.

And the Figure is from E the top of the Castle to F the side of the Tower at 10 degr. mounture, carries the Bullet violently 248 Paces.

Notes

• * 1.1

  Shooting by the Metal.
• * 1.2

  of Shooting by a Dispert.
• * 1.3

  To Shoot in a Right-Range, that is, as far as the Bullet doth go in a Right-line at any Degree of Elevation.

  By the Rule of Proportion.

  Paces.

  248	239519
  d.
  10:354	254900
  200	230703
  Sum	485003
  285	245484
• * 1.4

  Which done backwards, is 6 degr. against 285 in the last Table.