| Length of the | |||
| Weight of | moulds without | Interior diameter | Heights of the |
| Rockets. | their feet. | of the moulds. | nipples. |
| 6 lbs. | 34.7 inches. | 3.5 inches. | 1.5 inches. |
| 4 do. | 31.6 do. | 2.9 do. | 1.4 do. |
| 2 do. | 13.3 do. | 2.1 do. | 1.0 do. |
| 1 do. | 12.2 do. | 1.7 do. | 0.85 do. |
| 8 ozs. | 10.12 do. | 1.3 do. | 0.6 do. |
| 4 do. | 7.75 do. | 1.12 do. | 0.5 do. |
| 2 do. | 6.2 do. | 0.9 do. | 0.45 do. |
| 1 do. | 4.9 do. | 0.7 do. | 0.33 do. |
| ½ do. | 3.7 do. | 0.55 do. | 0.25 do. |
| 6 drs. | 3.5 do. | 0.5 do. | 0.22 do. |
| 4 do. | 2.2 do. | 0.3 do. | 0.2 do. |
By this table we find that a six-pound Rocket rammed solid, must be thirty-four inches, seven-tenths in length; its external diameter three inches five-tenths or three and half inches, and the height of the nipple one inch and a-half. The diameter of the nipple in this and all other cases must be equal to that of the former, and in regard to its height I have never found it to answer better than when the cavity which it formed at the mouth of the Rocket was hemispherical, or equal in height to half its diameter.
We shall now, by the following table, shew the method of finding the calibre of Rockets according to their weight, which is computed by the principles already given; that is, a pound Rocket is such that its aperture will just admit a bullet of a pound weight, and so of the rest.
Calibre and Weight of Rockets.
TABLE II.
Of the Calibre of Rockets of a Pound weight and below.
| 16 ounces. | 19½ lines.[10] | 14 drams. | 7¼ lines. |
| 12 do. | 17 do. | 12 do. | 7 do. |
| 8 do. | 15 do. | 10 do. | 6⅓ do. |
| 7 do. | 14¾ do. | 8 do. | 6¼ do. |
| 6 do. | 14¼ do. | 6 do. | 5⅔ do. |
| 5 do. | 13 do. | 4 do. | 4½ do. |
| 4 do. | 12⅓ do. | 2 do. | 3¾ do. |
| 3 do. | 11½ do. | ||
| 2 do. | 9⅙ do. | ||
| 1 do. | 6½ do. |
The use of this table will be easily understood, for, as in the first instance, if a Rocket of 16 ounces ought to be nineteen and a-half lines in diameter, one of 12 must be 17 lines, one of 8 ounces 15 lines, one of 8 drams six and a-quarter lines; and so of the others.
If the diameter of the Rocket be given, we can as easily, by the reverse method, find the weight of the ball corresponding to that calibre. For example, if the diameter be 15 lines, it will be immediately seen, by seeking for that number in the column of lines, that it answers to a ball of eight ounces.
As the foregoing table extends only to Rockets of 16 ounces, or one pound, and from that downwards, the following will be found equally useful for those of superior dimensions.