A sphere is, by no means, the best shape for a projectile; no one would think of making a roman candle star like a marble; the Minie bullets and the bolt-shot for our great guns are cylindrical, and far better fitted than globes for straight and rapid flight. Why not adopt the same shape for shells? I find cylindrical shells answer excellently. Have a former, for a small one, 21/2 inches diameter, and about 6 inches long, and with a handle like fig. 25. Roll a case upon it, 5 inches long, till the outside gauges 23/4 inches, or a trifle more. Turn a wooden bottom, 3/4 of an inch thick; half of it a tenon to fit the inside of the case, and half of it a flange, equal to the external diameter, a, fig. 95. Glue this firmly in, and farther secure it with 4 inch French nails; though, perhaps, this is not necessary. The top may be of the same shape; half-an-inch thickness will be sufficient. A hole, an inch in diameter, may be bored in it, with a centre-bit, to receive the fuse. This fuse may be a cotton reel, with one of the flanges sawed off, and the end filed slightly tapering, as fig. 105; the enveloping piece of calico, or glazed lining, can then be passed to the bottom, as indicated by the dotted lines; but a better way is to turn a piece of beech of the shape of fig. 96, with a collar, to prevent its being blown through, and a groove, by which the calico envelope can be tied. The length of the fuse may be about 11/4 inch; charge it by putting in very little at a time, and well mallet it. Pass a piece of naked match over the mouth of the fuse, and down the sides of the cylinder, as indicated by the dotted lines, fig. 95, having previously cut out a notch, at each corner, top and bottom, e, e, e, e, to guide it in a straight line. Take a piece of double-crown, about 20 inches long, and 7 broad; paste it all over, and roll the cylinder in it, in such a way that it shall be flush at top, and project at the bottom; press it round smooth with a cloth, or sponge, till the leaders form a vein on each side. When dry, invert it; put in the blowing powder; press the ends over, neatly, to form a bottom; and cover the whole with a circular piece of pasted paper. A shell of this size will hold forty gold rains, and a score or more blue stars, which have a very pretty effect. The head and the fuse may be in one solid piece, if preferred, as fig. 104; if the hole is longer than 11/4 inch, only 11/4 inch of it must be filled with fuse; a piece or two of match may fill up the rest. The mortar for this shell should be 18 or 20 inches high, and 3 inches internal diameter. The shell, when fitted up, will probably weigh about 14 or 15 ounces. The blowing powder may be 2 or 21/2 ounces of F grain, according to the fit in the mortar. The hole, in the wooden fuse, should be 3/8 of an inch diameter. See that the match is everywhere carefully covered. A shell of this size will be amply sufficient for amateur purposes. Perhaps it will be advisable to try a fuse an inch long the first time; it will be better that the shell should burst, while still ascending, than that it should pitch. One or two trials are, in all cases, necessary; but as these shells go a great height, they will bear a little longer fuse.
A cylinder holds half as much again as a shell of equal diameter; consequently, when the depth is twice the diameter, which is the best proportion, it holds three times as much as the spherical shell. If the latter be 3 inches diameter, it may be represented by the numbers 3 × 3 × 3 = 27. If the cylinder be 3 inches diameter, and 6 inches deep, it will be as 3 × 3 × 6 × 11/2 = 81. Practically, it will hold more, especially of rains, or serpents, as they pack better in a cylinder.
The spheroidal shell, like the spherical, is, also, 2/3 of its circumscribing cylinder.
Putting D, the diameter of a spherical; and d, that of a cylindrical shell, the length being always double the diameter; then D3 = 3 d3. Required the diameter of a cylindrical shell, that shall be of equal capacity with a spherical shell, of 12 inches diameter.
123 = 1728; 1728 ÷ 3 = 576 = d3, and
?576 = 8·3 = d.
so the cylindrical shell will be 83/10 inches diameter, and 163/5 inches long.
The same computation is more readily effected by multiplying the diameter by ?(1/3);
?(1/3) = ?(9/27) = 1/3 ?9 = ·693.
Then ·693 × 12 = 8·3, as before.
Shells, for war purposes, are both spherical and cylindrical; the latter are, sometimes, built up in pieces, which dovetail into each other; they are, then, set in a cylinder, and melted lead is poured round to bind the pieces together. For lighting up the country, to discover the movements of the enemy on a dark night, shells are fired, containing strong calico parachutes, carrying blue lights. Magnesium lights are, of course, more effective.
The bottoms and tops of the cylindrical shells, previously described, may be turned out of a plank of wood: elm, ash, common mahogany, or good yellow deal; and, as many amateurs who possess a lathe, know of no contrivance for holding flat pieces of board without making a hole through them, the following plan may be adopted. On the screw-chuck, fig. 102, screw a piece of deal board, previously sawn nearly circular, and as large as the lathe will take: let it be of a thickness to entirely hide the point of the screw; turn it to a circle; and over the face of it, with a blacklead pencil, while it is revolving, make a number of concentric circles, as in fig. 103. Also, cross it with two straight lines, passing through the centre, at right angles to each other. Cut the wood, intended for the bottom of the shell, into a square; make a hole at each corner, and with 4 screws, or 4 French nails, screw or nail it on the face: the concentric circles, and the two diametrical lines crossing them, will act as guides to centre it. I have thus been able to cut into a circle, in the lathe, so thin a substance as a piece of writing paper. It may be held on with 4 tin-tacks, or a touch of gum.
A nest of 6 or 9 little shells, each containing a separate colour, rains, serpents, crackers, &c., may be enclosed in a large shell: the fuse of these may be a very short piece of a squib-case, with the string wound 7 or 8 times round the choke, to form a flange, to prevent its blowing through.
Cylindrical shells should, of course, be filled before the head is glued in; this can have the fuse previously fixed in, and ready.
