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. XV. Of Iron Ordnance what quantity of Powder to allow for their Loading.

YOu must first Calculate a Charge of Powder for the said Iron Piece, as if it had been a Brass Piece, and in case you want the weight of the said Iron Piece, you must find it as you were taught in Chap. 7; and when you have found it as is taught in Chap. 9, how much Powder will Load the same if it were of Brass, then just 3 quarters so much is sufficient to Load an Iron Piece.

As for Example.

A Brass Saker of 1500 weight requires 4 l. what will an Iron Demi-Culvering of 2800 weight require? Work as in the 9 Chap. and you shall find 6 l. 6/10 or 6 l. 14 1/2 ounces, so well fortified as the Saker, will serve a Brass Demi-Culvering for a Charge.

The which we will likewise examine by the Rule in the 7 Chapter.

The Brass Saker's diam. is 3 35/100 inch. Logarithm	257403
The diam. of the Demi-Culvering Brass 4 50/100 inches	265321
The difference increasing.	7918 (3
The triple of the difference.	23754
The weight of the Saker added to it 1500	317609
gives the Logar. of the weight of of the Demi-C. Brass 2592 l.	341363

Or by the Scale, extend the Compasses from 3 75/100 to 4 50/109 the same distance turned 3 times from 1500, will reach 2592 l. as before.

The Arithmetical way.

4 50/100 C × 1500/3 ¾ C = is equal to the weight 2592 pound, which is the weight such a Demi-Culvering should be of that burneth 6 l. 14 ½ ounces of Powder.

To find what a Demiculvering of Brass of 28 hundred will require, Work thus.

The Logarithm of 2592	341363
The Logarithm of 2800	344715
The difference increasing.	3352
The one third of the difference,	1117
The weight in Powder 6 90/100 l. added	283884
gives the weight 7 l. 8 ounces	285001

Or extend the Compasses from 2592 to 2800, the same distance will reach from 6 9/10 to 7 ½ l. as before.

The Arithmetical way.

2800 × 6 9/10/2592 = 7 pound 8 ounces, as before.

Of which number you must take 3 Quarters for a Charge for the said Demi-Cul∣vering, ¾ thereof, being 5 pound 10 ounces, will be a sufficient Charge for such a Piece; and also whatsoever you find on the Scale, and in the Table in the third Chapter for Brass Pieces, take three quarters thereof for the Charge of your Iron Piece, if they be near that weight.