The sea-mans grammar and dictionary explaining all the difficult terms in navigation : and the practical navigator and gunner : in two parts / by Captain John Smith, sometimes governour of Virginia, and admiral of New England.

CHAP. XXIV.

Concerning a Gunner's Ruler, for the Elevating of any Piece of Ordnance to any degree of Mounture, supplying the Use of the Gunner's Quadrant.

FOrasmuch as a Quadrant can∣not at all times be conveni∣ently used; as when the Wind is high: Also in taking the depth or profundity of a Valley, or altitude of a Hill, &c. For the removing of all which inconveniencies this Gunner's Rule was invented, the Description and Figure whereof follow:

[illustration]

The. Gunners. Ruler. Standing. upon the Breech of a Peece

The Description of the RULER.

The Ruler may be of any length, with a large Slit in the middle for a Slider to move in, and in the Slider a Hole to look through: The Ruler must be slit quite through at the bottom, and a piece of Brass fastned over it; but at the top it may be left whole for half an Inch or more; in which whole part, a Nut may be fastned, through which a Screw must pass, to raise or depress the Slider as occasion requires: On both sides of the Slit, the Ruler must be divided into Feet and tenth parts of a Foot; and every one of those parts into 10 more, so then every Foot will be divided into 100 parts.—Through the Center of the little Hole, a small Line must be drawn quite thro' the Slider, which will shew at what height the Sight-hole standeth from the Base Ring of the Gun.—Also there must be an Index to hang on the edge of the Ruler, and under it a small Pin, perpendicular to the Pin on which the Index hangeth; which is to set the Ruler per∣pendicular or upright.

The Use of the RULER.

THe principal Use of the Ruler is (as I said before) to Elevate any Gun to any degree of Mounture. To per∣form which, there is to be used with the Ruler, this brief Table of Natural Sines following.

The use of the Table.

EXample 1. Suppose a Gun, which is 8 Foot, and 7 Tenths of a Foot Long, between the Base and Muzzle Rings, the which Gun being Mounted and Disparted, is to be Elevat∣ed to 2 Degrees and 6 Tenths of a Degree of Mounture.

A Table to be used with the Gunners Rule.

	Tenth Parts of a Degree of Mounture.
0	1	2	3	4	5	6	7	8	9
Whole Degrees of Mounture.
0	00000	00174	00349	00524	00698	00873	01047	01222	01396	01571
1	01745	01920	02094	02269	02443	02618	02792	02967	03141	03316
2	03490	03664	03839	04013	04188	04362	04536	04711	04885	05059
3	05833	05402	05582	05756	05931	06105	06279	06453	06627	06801
4	06975	07150	07324	07498	07672	07846	08020	08194	08368	08542
5	08715	08889	09063	09237	09411	09585	09758	09932	10106	10270
6	10452	10626	10780	10973	11147	11320	11494	11667	11840	12014
7	12187	12360	12533	12706	12880	13053	13226	13399	13572	13744
8	13917	14090	14263	14436	14608	14781	14954	15126	15299	15471
9	15643	15816	15988	16160	16333	16505	16677	16849	17021	17103
10	17365	17537	17708	17880	18052	18224	18395	18567	18738	18910
11	19081	19252	19423	19595	19766	19937	20108	20279	20450	20620
12	20791	20962	21132	21303	21474	21644	21814	21985	22155	22375
13	22495	22665	22835	23005	23175	23245	23514	23684	23853	24028
14	24192	24362	24531	24700	24869	25038	5207	25376	25545	25713
15	25882	26050	26219	26387	26556	26724	26892	27060	27228	27396
16	27564	27731	27899	28067	282••4	28401	2856••	28736	28903	29070
17	29237	29404	29571	29737	29904	30071	30237	30403	30570	30736
18	30902	31060	31233	31399	31565	31730	31896	32061	32227	32392
19	32557	32722	32887	33051	33216	33381	33545	33710	33874	••••••••8
20	34202	34366	34530	34694	34857	35021	35184	35375	35511	35674
21	35837	36000	36162	36325	36488	36650	36812	37002	37110	37295

Forasmuch as the Gun is to be elevated 2 degrees and 6 Tenth parts of a degree; Look for 2 degrees in the first Co∣lum of the Table, and for 6 parts of a degree in the head thereof; And against 2, and under 6, you shall find this Number, 04536, which multiply by 8. 7 (the length of the Gun in Feet and decimal parts of a Foot) the Product will be, 0394632. from which cut off (towards the right hand) five Figures for the Number taken out of the Table, and one for the 7 Tenths in length of the Gun, in all six Figures, then will the Product stand thus 0. 394632, which 0 to the left hand is no Feet, but the 3 following is 3 Tenth parts of a Foot, and the 9 following is 9 Tenths of a Tenth part of a Foot, which is neer 4 Tenth parts of a Foot, and to that Number on the sides of the Ruler, must the stroke (and hole) in the Slider be brought, and then the Ruler is rectified for that Ele∣vation

Exam. 2. Suppose a Cannon, whose Length is 11 Foot and 3 Tenths of a Foot, were to be Mounted to 14 deg. and 4 Tenths of a degree, to what divisions on the sides of the Ruler must the Slider be set?

Look in the first Columb of the Table for 14 deg. and for 3 Tenths in the head of the Table, so against 14, and under 4, you shall find this number 24869, which being multiplyed by 11. 3 Foot, the length of the Gun, the Pro∣duct will be 2810197; from which cut of 5 Figures for the number in the Table, and 1 for the 4 Tenths in the length of the Gun, it will stand thus 2. 810197, which is 2 Foot, and 8 Tenth parts of a Foot, and to that number on the Sides of the Ruler, must the Slider be set, to mount the Can∣non to 14. 4 deg. of Elevation.