Hence it is easy to conceive, that in order to fall at the greatest distance from the mortar, the bomb must be fired according to an elevation at the greatest possible distance, as well from a vertical, as from an horizontal line. This elevation divides in two equal parts the angle formed by the vertical and horizontal lines, which being of 90 degrees, or what is called a right angle, a bomb will be thrown to the greatest distance, in the direction of a line making an angle of 45 degrees. For above this angle the range will diminish, because the bomb approaches the vertical line; and under the same elevation it will also decrease, because the flight of the bomb approaches the horizontal line.
Hence also it appears that there are two angles, according to which a mortar may be inclined to make the bomb fall on the same place; these are the angles, equally distant from the line, which cuts the quadrant into two equal parts: so that if, for example, a mortar is elevated at 30°, the bomb will fall at the same distance as if it had been elevated at 60°, each of these angles being 15° distant on this, and that side of the quadrant; that is, from the angle of 45 degrees.
The second thing to be considered, is, to know the exact charge of powder necessary to throw a bomb to a given distance.
If the bomb, being fired at an elevation of 45°, falls short of the place intended, the charge of powder must be increased. If it reaches the place, or goes beyond it, it is evident that the charge is sufficient. If the bomb, at an elevation under 45°, fall short of the place intended, with a given charge, the mortar must be more elevated: if, on the contrary, it falls too far off, it must be more inclined to the horizon: and by these essays the proper degree of inclination may be easily and speedily discovered.
If the mortar then is raised above 45°, it must be more inclined, so as to make a more acute angle with the horizon, to increase the range of the bomb; and, on the contrary, raised nearer a perpendicular, to diminish it: all of which are consequences drawn from what has been said on this subject.
It must be observed, first, that the greatest distance to which a bomb can be thrown, with the strongest charge, is little more than about 1800, or 2000 fathoms.
Secondly, that though a mortar may be elevated indifferently, either so much above or below 45° as to carry a bomb to a given distance, yet when any building is to be destroyed, it should be raised above 45°, because the shell, rising to a greater height when fired according to a greater angle, falls with greater force, and by consequence will do more damage to the place on which it is thrown. But when the business is to fire on a body of men, the mortar must be pointed below 45°, that the bomb may not have force enough to enter far into the ground, and that the splinters in the explosion may do more execution.
| Practice for Sea-Mortars. | |||||||
|---|---|---|---|---|---|---|---|
| Nature of the Mortar. | |||||||
| 13 Inch. Powder. | 10 Inch. Powder. | Flight in Seconds. | Ranges in Yards. | Length of Composition in Fuses. | |||
| lb. | oz. | lb. | oz. | Inches | Parts | ||
| 3 | 0 | 12 | 612 | 2 | 64 | ||
| 4 | 0 | 1 | 12 | 14 | 832 | 3 | 8 |
| 2 | 4 | 15 | 958 | 3 | 30 | ||
| 5 | 0 | 2 | 6 | 16 | 1088 | 3 | 52 |
| 5 | 8 | 2 | 8 | 17 | 1299 | 3 | 74 |
| 3 | 2 | 18 | 1377 | 2 | 96 | ||
| 7 | 0 | 3 | 8 | 19 | 1534 | 4 | 18 |
| 4 | 0 | 20 | 1700 | 4 | 40 | ||
| 8 | 12 | 4 | 8 | 21 | 1874 | 4 | 62 |
| 9 | 0 | 5 | 8 | 22 | 2057 | 4 | 84 |
| 12 | 0 | 23 | 2248 | ||||
| 14 | 24 | 2448 | |||||
| 16 | 25 | 2656 | |||||
| 18 | 8 | 2 | 26 | 2873 | 5 | 72 | |
| 20 | 0 | 8 | 10 | 27 | 3098 | 5 | 94 |
| 22 | 0 | 9 | 8 | 28 | 3332 | 6 | 16 |
| 24 | 8 | 11 | 4 | 29 | 3574 | 6 | 38 |
| 28 | 0 | 12 | 0 | 30 | 3821 | 6 | 60 |
| 31 | 8 | 31 | 4085 | 6 | 82 | ||
The ranges of mortars, at the several elevations below, are in proportion to one another, viz.
| 45 | 40 | 35 | 30 | 25 | 20 | 15 | 10 | 5 |
| 100 | 98 | 94 | 86 | 76 | 64 | 50 | 34 | 17 |