19. Globes which Leap or Roll on the Ground.
Construct a hollow wooden globe of any dimensions at pleasure; it must be very round, both internal and external; its thickness must be equal to about the ninth part of its diameter. In this globe insert a small wooden cylinder, (A [fig. 28].) in breadth equal about one-fifth diameter of the globe, its thickness about half that of ditto: of the same size and opposite to this cylinder must be another aperture. It is through this latter aperture that fire is communicated to the globe, when it has been filled with the proper composition through the lower end of it; and by which you have the convenience of filling, and of putting, as is generally done, a petard or report of metal, filled with good grained powder over the inside of the aperture; besides this petard four or five others of a similar nature, only they need not be in metallic cases, are to be inserted; they must be loaded with good grained powder filled to their orifices. The composition for filling the remaining cavity of the globe is—one pound of bruised gunpowder, six pounds of salt-petre, three pounds of sulphur, two pounds of iron-filings, and half a pound of Greek pitch. This composition will not require much grinding or sifting; it will be sufficient if the different ingredients be well incorporated. It should not be made up quite dry, but with a little of one of the liquids we have before mentioned.
A globe prepared as above, on being fired by means of a match attached to the orifice A, will leap and bound about as it burns, or according to the accidental explosion of the petards, which are set on fire by the composition.
Instead of placing these petards in the inside, they may be affixed to the exterior surface of the globe, which they will make to roll and leap about as they successively take fire. They may be arranged in any manner on the surface of the globe, providing a connection is formed between them by means of leaders.
Many differences in the arrangement and form of these globes may be made, and which will readily suggest themselves to the ingenious practitioner; such as an arrangement of rockets on the inside, laid head and tail together; but in case the globe should be of paper or pasteboard, made in two equal hemispheres, and joined together by paper, the match must be applied through a hole in the globe made opposite the mouth of the first rocket; these rockets should have no petards at their tops. It must here be observed that the globes must be perforated in various parts, otherwise they will burst by the combustion of the composition.
When used as water globes, care must be taken to seal and plug up the lower aperture I, K, first with a tompion, or plug of wood, and afterwards with some melted pitch; which latter may be put all over the globe in order to preserve it from the water. Over the plug at bottom, and previous to the application of the pitch, must be melted such a quantity of lead, as will cause the globe to sink in water, till nothing but the part A, will remain above its surface; this will be the case when the weight of the globe and its contents, with the lead attached, becomes equal to the weight of an equal volume of water. If the globe be then placed in the water, the lead by its superior gravity, will make the aperture I, K, tend directly downwards, and keep in a perpendicular position the cylinder A, to which fire must have been previously applied.
Trial should be made respecting the quantity of lead previous to its being exhibited, which may be easily done. The figures referred to represent a globe under various modes of arrangement.
Moon and seven Stars.
20. Moon and Seven Stars.