It is possible also, and that without difficulty, if the water is deep enough, to fire the water rocket as a sky rocket, vertically. In this case the stick must be counterpoised at the bottom by a bit of lead, so that the rocket may float erect, and as the mouth may be immers ed, a leader must also be conducted from it upwards. Rockets so disposed, ascend with great force at first, owing to the great resistance offered by the water to the issuing stream of air.
Instead of single water rockets of a large size, many may be fired together ; and in this case they are called squibs. These differ in no respect in their construc tion from ordinary squibs or serpents ; only care must be taken that they may always float. In discharging them, some precautions are also required. The whole must he collected together on a piece of light-wood, by means of two or three stands of quick-match, which, being burnt when they are lighted, they can easily dis engage themselves, and wander about on the water.
If it is wished to fire large reports under water, these must be made in maroon cases of unusual size, and so heavy us to sink. A bit of squib or port-fire may then be attached to each, which is lighted when they are thrown in. This continues to burn under the water, however imperceptibly, so that the explosion of the cracker is somewhat unexpected and surprising, al though the report is hollow, and as if suffocated If very large, it produces a sensible shock on the surround ing ground. These crackers may also be floated, and exploded upon the surface.
We may lastly add, on the subject of the simpler water rockets; that Roman candles, gfrbcs, cases of serpents or of stars, or an) kind of fixer; cases that are used on the ground, may also be fired from the surface of the water by means of proper floats ; but the method of doing this is so simple as to require no particular description, though we may remark, that large white lights calculated to burn for a considerable time produce a very pleasing effect in this way.
The simple water rockets may also be combined like the line rockets, so as to produce a more durable and various effect. Thus two or three, or many more, may be united in alternate order, so as that one may fire when the other is expended. But as the water permits of motion in any direction, we arc not even limited to this regular order. Thus the cases may be put together in any disorderly manner that the operator chooses, and the effect of this will be a great variety of intricate serpen tine movements, so as to increase very much the effect ; the greatest objection to the water rocket being its want of variety and brilliancy. If they are attached in the form
of a wheel, so as to float on the surface, they will also produce a pleasing appearance ; but the artist must not expect that they will revolve regularly like a wheel in this manner, because of the very unequal resistance which they meet with from the water in the attempt to revolve. 1 o make a wheel revolve upon water requires a proper contrivance, which must be sufficient to float whatever wheels may be used. We shall describe tin der the head of Wheels all the kinds, so that the artist may select from them any which he may think proper.
Of Gerber.
This is the most brilliant of all the fixed simple fire works, being formed entirely of the iron fire. See plate CCCULXX1. fig. 10. Various receipts for it will be found in the table of compositions, so that we need not here repeat them. We must, however, remark, that in proportion to the dimensions of the gerbe may be the size of the particles of iron. Thus the largest frag ments of cast iron may be put into cases of three or four inches in diameter, while steel filings may be used for the smallest. The proportion of three pounds of mealed powder to one of iron will be found to answer generally as a rule.
There is a peculiarity in the construction of the cases for the larger gerbes which requires to be described. They should be extremely strong, as the composition, which is very powerful, and requires to be much checked at the issue, might otherwise burst them. But besides the ordinary choke, they must be provided with a second at some distance, and as this is some what difficult to manage in paper, it is better to have a vacant space in the case above the choke, which is to be filled with a wooden tube, well glued, and secured in it ; the diameter of its bore being the same as that of the choke itself. This may be about two inches in length for the cube of three or four inches in diameter, and so in proportion; the smallest sizes requiring no thing more than the ordinary choke. The purposes of this long aperture is to enable the iron to be complete ly heated in its passage out, without which precaution the larger kinds might be thrown out unburnt; and also to compel the sparks to spread over their issue, so as to produce that resemblance of a wheat sheaf whence the name is derived.