The same kind of simple stand answers the purpose, also, on shore, when rockets are fired for amusement. But, as in most of those cases, there are commonly crowds of people collected, who might be endangered by the falling cf the sticks, it is necessary to throw the rockets so far off from the perpendicular as to avoid all hazard of their falling back into the crowd when they are burnt out. In the same way, the engineer may choose some piece of ground where they may fall with the least injury, avoiding houses, or places where there may be corn or hay, or other combustibles, and choos ing a piece of open meadow ground, or other naked land. By knowing the altitude of ascent, it is very easy to compute the necessary inclination for this pur : pose, without, at the same time, causing the rocket to not sufficient to introduce any error into a computa tion formed on this basis, greater than those which would arise from an actual measurement of the vertical ascents.
On the Firing of Rockets, deviate so far from the vertical line as to its effect. Spectators always judge of the perlecuon of a racket by the perpendicularity of its flight, unaware that this can never be attempted without the greatest risk of injury to themselves.
This danger is far from imaginary; even in the half pound rocket, the fall of the stick, from a bight of 400 yards, is sufficient to give a very hard blow. The weight of the one pounder stick, descending from its usual height of 500 yards, is very considerable, and in deed sufficient to kill a man. They have been known to break an arm, and after that to penetrate deeply into the ground. We have seen them pass through both the wooden sides of a drum, which is made of a very tough ash hoop, and then enter the earth to a foot in depth.
For this reason, when flights of rockets are fired, as there are generally crowds present, and as it is impos sible to regulate their directions, these should never ex ceed half a pound ; but even the quarter pound size is preferable. These are sufficiently showy ; they ascend 300 yards, and the fall of the sticks can do little harm, unless a chance spectator should receive one in his face. Fortunately, they generally retain fire enough to fore warn idle people of this kind of danger.
The last circumstances which we shall notice re specting the firing of rockets] are the methods which have been proposed for increasing their range or ascent. It is evident, on the slightest inspection of a rocket when about to rise, that a very large portion of the com position is burnt before it is able to quit its place, or, in mathematical language, there is a considerable portion ol the force eXpt mica Ili uvr..la,.. • 5 Lie iner tia, just as there is when a team of horses first attempts to set a waggon in motion. When once the motion has commenced, a very small addition of force is suffi cient, not only to sustain the velocity against the re sistance of the air and the force of gravity, but to add to it progressively till it has attained the maximum, or till all these forces are balanced. Now, if the initial
velocity, or any velocity could be communicated at the beginning, all that would be saved in the burning of the composition, and, consequently, the extent of range or ol ascent, would be proportionally augmented. This is but an imaginary advantage, as we shall immediate ly show. Let the mean times of flight and elevation of the one pound signal rockets be taken, respectively, at twelve seconds and 500 yards, which is near enough to the truth. Novi, in firing, about two seconds are expended on tht. post, in the attempts to first overcome the inertia ol the rocket, and two more in comniunicat ing to it a velocity considerably short of the greatest which it will acquire. We may therefore consider three seconds expended in overcoming the inertia, or in placing the rocket in a state to derive all the advantages which it might from its own power of flight. This amounts to just one-fourth of the whole time of burn ing It must not, however, be considered as accurate ly representing the time which is I st to the flight, as the rocket does not acquire its full force till the bore has become so much enlarged by the fire as to give issue to a considerable torrent of fire, or, correctly speaking, stream of air. Were we to consider it as a true measure of the loss of range, we should find that the pound rocket, burning twelve seconds, and rising 500 yards, would lose a fourth part of its range, or 122 yarOs nearly ; but we shall probably not be very wide of the ituth if we take it at 80 But if this is not of much moment in ornamental rock ets, or even in those used for signals, it is of considera ble consequence in military or projectile ones, in which the length of range is of great inipoli2nce. And if we attend to the nature of the curve formed by the flight of the rocket at 45°, we shall find that the variations in the amplitude of projection, or in the actual random, ale of even more moment than those in the perpendi cular ascent. The same reasoning applies to those cases in which rockets have been used to throw out lines to ships in distress on a Ice shore. Now, it has been attempted to overcome this inertia, or communicate an initial velocity by firing the rockets from a piece of ordnance. But the blast of the powder ruins the com position, and frequently breaks it, so as to cause the rocket to blow up in the piece, or in the frame where it is fired. This, in the case of the iron rockets in parti cular, is a very dangerous accident, which renders them almost as formidable to the artificers as to the enemy ; and it has in more than one instance been attended with fatal results.