To cause a Rocket to form an arc in rising.

11. TO CAUSE A ROCKET TO FORM AN ARC IN RISING.

Cut some circles, about three or four inches diameter, out of some tin, or other thin plate; then to the rod of each Rocket, and about twice the length of the case from its mouth, fix one of these pieces of tin, nearly at right angles from the rod, and make it quite fast by a bracket underneath. The fire acting upon this, as it proceeds from the mouth of the Rocket, will divide the tail in such a manner, that it will cause it to proceed in a circular course, and form a very pleasing appearance.

To fire Rockets without Rods.

12. TO FIRE ROCKETS WITHOUT RODS.

Rockets may be made to rise in the air without rods, but in the place of which, they must have attached to them four triangular pasteboard wings, fixed lengthwise on the external of the cartridge, similar to those attached to arrows or darts. The length of these wings should be about three-fourths the length of the Rocket; their breadth at bottom should be half their length, and diminished off to nothing at top. The Rocket may be set over a hole in a board, and fired from the under side; or the four wings may rest on four iron pins, six or eight inches in length, drove into a board at suitable distances from each other, and the Rocket fired from between them.

Though the greatest care be employed in the exhibition of Rockets after this manner, still their ascent is by far less certain than when a rod is used; therefore the Tyro must not be disappointed if he chance to fail of success.

Theory of the flight of Rockets.

THEORY OF THE FLIGHT OF ROCKETS.

A Rocket, being properly constructed, with its rod and other appendages attached, fixed in a vertical position, and fire being applied to its mouth, it will (as experience proves) ascend in the air with a prodigious velocity: but upon inquiry into the cause of this ascent, we meet with difficulties little contemplated when we were viewing the beautiful path it described in the medium of its flight.

That this ascent is dependent on the medium (or air) in which it is generated, admits not of a doubt; but to describe how, or in what manner it is effected, has engaged the attention of some of the most eminent philosophers. In consequence several theories have been advanced for the explication of the phenomena, and among them those of Mariotte and Desaguliers have claimed the most particular attention.

Mariotte attributes the rise of Rockets to the resistance, or reaction of the air against the gas, which is generated by the combustion of the composition.

This hypothesis seems to explain the phenomena; but great objections have been brought against it, on account of the difficulty which attends the reduction of it to mathematical investigations:—this difficulty arises from the law which the propelling force must necessarily observe; that is, it will decrease as the velocity increases, in consequence of the partial vacuum left behind the Rocket in its flight; so that the velocity becomes as it were both a datum and quæsitum; and the correct solution of the problem necessarily involves the integration of partial differences of the highest order.

The hypothesis of Desaguliers is somewhat different to the foregoing; it is much more familiar with mathematical investigations; as it reduces the whole theory to the most simple form; and we think it is not far from being consonant with the known principles of the phenomena; notwithstanding the argument brought against it by Dr. Rees, and his Editors; and which we shall endeavour to prove by citing higher authority than our own.

Dr. Desaguliers illustrates his hypothesis in the following manner:—Conceive the Rocket to have no vent at the choak, and to be set on fire in the conical bore; the consequence would be, either that the Rocket would burst in the weakest place, or that, if all parts were equally strong, and able to sustain the impulse of the flame, the Rocket would burn out immoveable. Now, as the force of the flame is equable, 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.

Imagine then the Rocket opened at the choak; by this mean 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 it is tied to.

Accordingly we 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 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.

To this we shall add the late Doctor Hutton’s philosophy, on the ascent of Rockets; who 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 escapes 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 one of these forces over the other.

This, however, would not be the case, unless the Rocket was pierced to a certain depth. A sufficient quantity of elastic fluid would not be produced; for the composition would inflame only in circular coats, of a diameter equal to that of the Rocket; and experience shows that this is not sufficient. Recourse then is had to the very ingenious idea of piercing the Rocket in a conical hole, which makes the composition burn in conical strata, which have much greater surface, and produce a much greater quantity of inflamed matter and fluid. This expedient was certainly not the work of a moment.

The stick serves to keep it perpendicular; for if the Rocket should begin to tumble, moving round a point in the choak, as being the common centre of gravity of Rocket and stick, there would be so much friction against the air by the stick, between the centre and the point, and the point would beat against the air with so much velocity, that the reaction of the medium would restore it to its perpendicularity. When the composition is burnt out, and the impulse upwards has ceased, the common centre of gravity is brought lower towards the middle of the stick, by which means the velocity of the point of the stick is decreased, and that at the point of the Rocket is increased; so that the whole will fall down, with the Rocket end foremost.

During the time the Rocket burns, the common centre of gravity is shifting and getting downwards, and still faster and lower as the stick is lighter; so that it sometimes begins to tumble before it is quite burnt out: but when the stick is too heavy, the common centre of gravity will not get so low, but that of the Rocket will rise straight, though not so fast.

From the experiments of Mr. Robins, and other Gentlemen, it was found that the Rockets of two, three, or four inches diameter, rise the highest; and they are found to rise to all heights in the air, from 400 to 1,254 yards, which is about three-quarters of a mile. For further particulars respecting the theory of the flight of Rockets our readers are referred to Robins’s Tracts, vol. 2.—Philosophical Transactions, vol. 46, page 578: and more particularly to Mr. W. Moor’s “Treatise on the motion of Rockets,” in which they will find the subject elegantly treated.