led to the platform. "I declare there is a forest of rockets! and what magnificent Pinwheels, Tourbillions, Marroons, Pots des Aigrettes, Gerbes, Courantins, and Roman Candles."

"Are those paper cylinders, with long sticks, rockets?" enquired Tom.

"They are; and if you will attend to me, I will explain the principle of their construction. They have ever been considered as holding the first place amongst single fire-works, and deservedly so; not only on account of the splendid appearance they present when fired by themselves, but from their extensive application in increasing the beauty of other exhibitions. The rocket, you perceive, consists of a strong paper cylinder, which is filled with a suitable composition; it is crowned with a head, or 'pot,' as it is technically termed, charged with various materials, which throw out sparks, stars, and other decorations, as soon as it takes fire in the air, after the body of the rocket has been consumed. You may observe that the head is made to terminate in a point, which greatly facilitates its passage through the air. The whole is affixed to a straight stick, which, like the rudder of a ship, makes it turn towards that side to which

it is inclined, and consequently causes the rocket to ascend in a straight line."

"But, papa," observed Louisa, "all the rockets have not straight rods; see, there is one with a crooked stick."

"That is for the purpose of causing the rocket to ascend in the form of a screw: the first effect of the bent rod will be to make the rocket incline towards that side to which it is bent; but its centre of gravity bringing it afterwards into a vertical situation, the result of these two opposite efforts will be, that the rocket will ascend in a zig-zag or spiral form. In this case, however, since it displaces a greater volume of air, and describes a longer line, it will not ascend so high as if it had been impelled in a straight direction; but I think you will admit that, on account of the singularity of this motion, it produces a very agreeable effect."

“And what causes the rocket to ascend into the air?" asked Tom.

"That is a question much more readily asked than answered," replied Mr. Seymour: "it is a subject which has engaged the attention of several most distinguished philosophers.

I

shall first describe to you the theory of Desaguliers. He says, 'Let us suppose that the interior of the rocket were inflamed, and that there were not any vent for the fire; the consequence would be, either that the rocket would burst in the weakest part; or, if all the parts were equally strong, and able to sustain the impulse of the fire, that the rocket would burn out without any motion. Now, as the force is equal in all directions, suppose its action downwards, or that upwards, sufficient to lift forty pounds; as these forces are equal, but their directions contrary, they will destroy each other's action. In the next place, imagine the rocket opened at the choak; in consequence of which the action of the flame downwards is taken away, and there remains a force equal to forty pounds acting upwards, to carry up the rocket, and the stick or rod to which it is attached. We accordingly find that if the composition of the rocket be very weak, so as not to give an impulse greater than the weight of the rocket and its stick, it does not rise at all; or if the composition be slow, so that a small part of it only kindles at first, the rocket will not rise.' Dr. Hutton explains the phenomenon in some

what different a manner.

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 more simple and plausible, than that of Desaguliers.

“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."

"What are those fire-works, attached to the lines?" asked Tom.'

"Those, my dear, are line-rockets, or courantines, 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.”

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"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.”

* From the French term courant, signifying running.