DEPARTMENT OF AUTOMOBILES, BOMBS, AND MOVIES |
| DIRECTOR Barnaby Milosevic |
ABOUT
These globes are called aerials, because they are thrown into the air from a mortar, which is a short thick piece of artillery of a large calibre.
Though these globes are of wood, and have a suitable thickness, namely, equal to the twelfth part of their diameters, if too much powder be put into the mortar, they will not be able to resist its force; the charge of powder therefore must be proportioned to the globe to be ejected. The usual quantity is an ounce of powder for a globe of four pounds weight; two ounces for one of eight, and so on.
As the chamber of the mortar may be too large to contain the exact quantity of powder sufficient for the fire ball, which ought to be placed immediately above the powder, in order that it may be expelled and set on fire at the same time, another mortar may be constructed of wood, or of pasteboard with a wooden bottom, as Ab, fig. 13, pl. 1: it ought to be put into a large iron mortar, and to be loaded with a quantity of powder proportioned to the weight of the globe.
This small mortar must be of light wood, or of paper pasted together, and rolled up in the form of a cylinder, or truncated cone, the bottom excepted; which, as alreadv said, must be of wood. The chamber for the powder Ac must be pierced obliquely, with a small gimblet, as seen at Be ; so that the aperture B, corresponding to the aperture of the metal mortar, the fire applied to the latter may be communicated to the powder which is at the bottom of the chamber Ac, immediately below the globe. By these means the globe will catch fire, and make an agreeable noise as it rises into the air; but it would not succeed so well, if any vacuity were left between the powder and the globe.
A profile or perpendicular section of such a globe is represented by the right-angled parallelogram Abcd, fig. 13 n°. 2; the breadth of which Ab is nearly equal to the height Ad. The thickness of the wood, towards the two sides, L, M, is equal, as above said, to the twelfth part of the diameter of the globe; and the thickness, Ef, of the cover, is double the preceding, or equal to a sixth part of the diameter. The height Gk or Hi of the chamber, Ghik, where the match is applied, and which is terminated by the semicircle Lgii.m, is equal to the fourth part of the breadth Ab ; and its breadth Gh is equal to the sixth part of Ab.
We must here observe that it is dangerous to put wooden covers, such as Ef, on aerial balloons or globes; for these covers may be so heavy, as to wound those on whom they happen to fall. It will be sufficient to place turf or hay above the globe, in order that the powder may experience some resistance.
The globe must be filled with several pieces of cane or common reed, equal in length to the interior .height of the globe, and charged with a slow composition, made of three ounces of pounded gunpowder, an ounce of sulphur moistened with a small quantity of petroleum oil, and two ounces of charcoal; and in order that these reeds or canes may catch fire sooner, and with more facility, they must be charged at the lower ends, which rest on the bottom of the globe, with pulverised gunpowder moistened in the same manner with petroleum oil, or well besprinkled with brandy, and then dried. N.G.