Composition for Serpents, for trimming Signal Rockets.
| Meal-powder, | 16 | parts. |
| Saltpetre, | 3 | —— |
| Sulphur, | 2 | —— |
| Charcoal, | ½ | —— |
The star composition is the same as before given.[36] It is mixed and made into balls or cubes, in the same manner. The petards or crackers are small cubes of paper, filled with grained gunpowder. They are wrapped with two layers of good thread, which is drawn tight in every direction. They are dipped in tar to give them more consistence, and pierced and primed with quick match. We have already given the theory of the flight of rockets in the first part of this work; and also the opinions of Mariotte and Dr. Desaguliers. On this head, therefore, further observation seems unnecessary We have said, however, that it is necessary, for giving the rocket a sufficient degree of motion, that the powder within the rocket be bored with a tapering cavity from the choke, and at the choke this cavity must be as wide as the choke itself, and at the further end, not more than half that width. The length of this bore must be but one inner diameter of the rocket, short of the whole height to which the rocket is rammed. The use of this bore, it is to be observed, is to increase the surface, that takes fire at once; that a greater body of fire may issue out of the mouth of the rocket. From the vehemence with which the fire issues out, the rocket receives its motion. We have seen, that rockets are used in all fire-works that have motion; for cases charged give motion to wheels of various kinds, and act on the same principle. Such works as are thrown into the air after the manner of bombs, are, however, an exception.
The rocket-stick is a necessary appendage. When very heavy, to prevent mischief by their fall, they now bore the sticks, and fill them with powder, that they may shiver in the air before they fall.
That the stick keeps the rocket perpendicular is obvious. If the rocket should begin to tumble, moving round a point in the choke, 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. Hence the velocity of the point of the stick is decreased, and that of the point of the rocket increased; so that the whole will tumble down, with the rocket end foremost. During the combustion of the rocket, the common centre of gravity is shifting and getting downwards, and faster and lower as the stick is lighter.
In the Philosophical Transactions, (vol. xlvi, p. 578) and Robins's Mathematical Tracts, (vol. i, p. 317, &c.) are sundry experiments, and observations concerning the flight of rockets; and as these experiments appertain more to military purposes, the following extracts may, on that account, be useful.
Mr. Robins, considering the great use that may be made of rockets, in determining the position of distant places, and in giving signals for naval and military purposes, procured some, with a view of ascertaining the height to which they rise, and the distance at which they may be seen. The greatest part of them did not rise to above four hundred yards; one to about five hundred; and one to six hundred yards nearly. The greatest distance at which these were observed, was from thirty-five to thirty-eight miles. Others were fired at a different time, one of which rose to six hundred and ninety yards; and it was observed, that the largest, which were about two and a half inches in diameter, rose the highest. In some subsequent experiments, conducted by Mr. Da Costa, Mr. Banks, &c. it was found, that, of two rockets, of about three and a half inches in diameter, one rose to about eight hundred and thirty-three, and the other to 915 yards. In another trial, a rocket of four inches in diameter rose to one thousand one hundred and ninety yards. In other experiments, a rocket of one and a half inches rose to seven hundred and forty-three yards; one of two inches to six hundred and fifty nine; one of two and a half inches to eight hundred and eighty; another of the same size to one thousand and seventy-one; one of three inches to one thousand two hundred and fifty-four; one of three and a half inches to one thousand one hundred and nine; and one of four inches rose to seven hundred yards, and, turning, fell to the ground before it went out. Besides these, there was one of the rockets of "twenty-four inches in diameter,"[37] which rose to seven hundred and eighty four yards, and another of the same size, to eight hundred and thirty-three yards. From these experiments, it is inferred, that rockets from two and a half to three and a half inches in diameter, are sufficient to answer all the purposes for which they are intended; and they may be made to rise to a height, and to afford a light capable of being seen to considerably greater distances than those just mentioned.
Before we mention the war-rockets of Congreve, it may not be improper to speak of the Indian rockets, which are used by the native troops of India, and which were employed against the British, with great effect, during the seige of Seringapatam in 1799. These rockets are made of iron, and are lashed to a bamboo cane. The weight is seldom more than two pounds, or less than one. The fougette, or Indian rocket, resembles in shape a sky-rocket, whose flight is gradually brought to run along a horizontal direction. By throwing several fougettes into parks of artillery, and upon caissons, &c. considerable damage might be occasioned from the fire, which would inevitably be communicated to some part. A fougette forces itself immediately forward, cuts as it penetrates, by the formation of its sides, which are filled with small spikes, becomes combustible, and on fire at all its points, and possesses within itself a thousand different means, by which it can adhere to whatever object it is destined to set on fire or destroy. A French writer even asserts, that this weapon would be more effectual, because it might be more variously applied, to defend the mouth of a harbour against an enemy's shipping, than red-hot balls can ever prove; and we are also told, that, by means of their natural velocity, they would do more execution, in a less space of time, than the most active piece of ordnance could effect; and they would also require fewer hands, as the only necessary operation would be to light and dart them forward.
The fougette, called also in French the Baguette à feu, has received improvements in France, which we will notice hereafter. In favour of these improvements and their application, we are told, that, to do execution at a distance, especially in sea-fights, fougettes may be so made as that they may reach shipping at a great distance, and with a given velocity.