“And what causes the rocket to ascend into the air?” asked Tom.
“It is a subject which has engaged the attention of several most distinguished philosophers; the explanation, however, offered by Dr. Hutton appears to me to be the most satisfactory. He says, ‘that at the moment when the powder begins to inflame, its expansion produces a torrent of elastic fluid, which acts in every direction; that is, against the air which opposes its escape from the cartridge, and against the upper part of the rocket; but the resistance of the air is more considerable than the weight of the rocket, on account of the extreme rapidity with which the elastic fluid issues through the neck of the rocket to throw itself downwards, and therefore the rocket ascends by the excess of the one of these forces over the other.’”
Tom observed, that he thought Dr. Hutton’s explanation very simple and plausible.
“Dr. Hutton adds,” continued Mr. Seymour, “that the rocket could not rise unless a sufficient quantity of elastic fluid were produced, and hence arose the expedient of piercing the rocket with a conical hole, so as to make the composition burn in conical strata, which, having much greater surface, produce a much greater quantity of inflamed matter and elastic fluid. Without such a contrivance, the composition would inflame only in circular coats of a diameter equal to that of the rocket; and experience has shown that this is not sufficient for the purpose. Some years ago a plan was suggested for producing the propulsion of a vessel in this way; by the force of a steam-engine, a stream of water was to be shot out of the stern, the impulse of which, upon the water in the river, was to push forward the boat. It is a curious fact, that Nature has employed the same expedient for the motion of some aquatic insects. The larva of the dragon-fly, according to Adams, swims forward by ejecting water from its tail.”
“What are those fire-works, attached to the lines?” asked Tom.
“Those, my dear, are line-rockets, or courantines,[[81]] and which, instead of rising into the air, run along the line, to which they are attached by means of a hollow cylinder. Their motion is to be explained upon the same principle as that of the sky-rocket; a force is generated by the escape of elastic matter, and as the rocket is confined to the rope, it is made to run along the line, instead of ascending into the air.”
“That is clear enough,” said Louisa; “but see, papa, there is the figure of a dragon on yonder rope!”
“That is merely a runner for the courantine, which is constructed in that form, for the purpose of rendering the exhibition more surprising. I dare say it is filled with various compositions, such as golden rain, and fires of different colours, which will greatly heighten the effect: indeed this pyrotechnic amusement may be infinitely varied.”
“Are not those pin-wheels, which are elevated above the railing?” said Tom.
“Yes; they are pin or Catharine wheels, and if you will look at them, you will perceive that they are of very simple construction; consisting merely of a long paper tube, filled with inflammable matter, and rolled round a small circle of wood, so as to form a helix or spiral line.”