Shells are hollow paper globes, fired vertically, from mortars, or iron tubes. They are made of various sizes, from 3 inches in diameter to 16 inches. To make a 3-inch shell. Turn a wooden ball, 3 inches diameter; and, round the middle, that is, the equatorial circumference, cut a V groove, or triangular channel, deep enough to receive a piece of raw or naked match. Remove it from the lathe, and cut it into two halves at right angles to the groove, that is, round a meridional circumference. Construct a deal box, 4 inches square, 2 inches deep. Place one of the half globes, flat surface downwards, on the middle of the bottom of the box, and secure it with screws from underneath. Brush it, and the inside of the box, all over, with sweet oil, with a camel's-hair pencil. Put some water into a basin; sprinkle into it as much plaster of paris as judged necessary; about 4 tablespoonfuls; pour off the water which floats above; stir up the plaster till homogeneous; pour it into the box; and, with a sash-tool held upright, beat the plaster in with the points of the bristles. Leave it to set.

Instead of having a wooden ball turned, a hemispherical concavity may be made by pressing, half way, into sand, one of the painted india-rubber balls sold at the toyshops; and pouring plaster over it. Or, a basin, an inch diameter larger than the intended shell, can have the plaster mixed up in it, till about three-parts full; and then the bottom of an oil flask can be pressed into it. A narrow strip of blue paper should be previously pasted round the oil flask, at the proper height, as a guide to know the proper depth to which it may be pressed. The plaster, when partly dry, must be neatly trimmed; and may be left, permanently, in the basin. Or, a stiff paper cylinder, or a tin cylinder, may be made, an inch larger in diameter than the diameter of the intended shell: put the oil flask into this, neck downwards, and pour in dry sand, till only the hemispherical bottom of the flask is left exposed; level the sand; oil the flask; and pour in plaster, as before. Be careful that the mould is not less than half-an-inch thick in any part. Or, one or two, or more halves of the zinc, or copper globes, used for ball-taps, may be obtained of the plumber, and used for moulds, without further preparation.

To Make the Shells.

Procure two kinds of paper; one imperial brown; the other sugar paper, printed paper, paper hangings, or any paper of a different colour from brown. The shell is supposed to be 3 inches; half as much again is 4¹/₂; add to this 1¹/₂ for a flange, gives 6. Cut out a circular piece of the brown paper, 6 inches in diameter. Snip it all round with the scissors, in slits, reaching from the circumference, half way towards the centre; soak it in water, and lay it on a towel to drain. Have a piece of sponge, about the size of an orange; soak it also, and wring it. Place the piece of brown paper in the plaster concavity, and press it in neatly with the sponge, in all directions; it will fill up the mould, and overhang all round; press the overhanging part flat, so that it forms a flange. Cut a piece of another coloured paper, into a strip, about 2 inches broad, and paste it well; then cut it across, backward and forward, like the letter W, which will reduce it to V-shaped triangles. Take these up, one by one; lay them in the brown paper, pasted side downwards, and press them neatly in with the sponge, making each slightly overlap the other. Let these also overhang to thicken the flange. This being done, proceed with a layer of brown; and so on, alternately, till it gauges about 2³/₄ inches across. The shell will, then, be about ¹/₈ of an inch thick. Remove it, and proceed with others. The different-coloured papers enable the eye to detect, in a moment, whether any part is left uncovered. When dry, cut off the flange; make the edge straight: rub it on a sheet of glass paper, spread flat on a board. With a ⁹/₁₆ inch punch, cut a hole in the middle of one hemisphere; to it, glue another hemisphere: and cover with two more layers of paper, or pieces of calico. The shell may, then, when dry, be filled with any kind of stars, or rains, that can be got through the hole. Along with the stars put ¹/₁₆ of their weight of meal powder for a bursting charge: that is, if the stars weigh 4 ounces, as they probably will, put 4 drams of mealpowder. Charge a roman candle case, ³/₈ inch internal, 4¹/₂/8 external diameter, with shell fuse (see fig. 59); saw it into inch lengths. Cut a piece of calico, 2 inches broad, and long enough to go twice round the fuse: paste the calico all over, and roll the fuse in it, so that the envelope is flush at one end, and overhangs one inch at the other. Glue this in the hole of the shell, the flush end, a, fig. 93, of course, inward: the enveloped end, b, being to receive the match, ³/₄ of the fuse may be pushed in, ¹/₄ of an inch left to project. With a printer's bodkin, or a stiletto, make a hole through both sides of the envelope, as at c and d; these holes are to be in a line with the groove; put through them a piece of raw match, in such a manner that it shall lie across the mouth of the fuse, and go, in the groove, round the shell underneath, and reach to e and f. Paste strips of paper over the match, the same as with tourbillions and saxons; or, the part of the match lying in the groove, may be in a leader pipe. Weigh the shell, and take about ¹/₅ of its weight of coarse grain powder, for a blowing charge. Make a cone of two or three thicknesses of paper; put the blowing charge into it; stick the cone on the bottom of the shell, and set by to dry. In the calico mouth of the fuse, tie a long piece of leadered match, and paste a strip of paper round, to make secure. If the mould has been made with the indentation of an oil flask, or with the globe of a ball-tap, it will, of course, not have a groove to receive the match; but this is of little consequence; the match can be drawn round outside, and covered, so as to appear as it does on tourbillions and saxons, like a vein on the back of the hand, when the fingers are held downwards.

Formerly mortars were made of sheet iron, riveted and bound round with cord, which latter would not prevent them cracking, if they were not thick enough: they are now made on an improved principle: the iron is rolled, by powerful machinery, of three thicknesses, exactly like a squib case; it is, then, made white-hot, and the three are welded together, with a steam hammer. Large mortars, also, have an iron bottom, or breech fixed in them, and are farther strengthened with a couple of rings, put on hot, and shrunk by cold, like tires on wheels; a third ring is put over the other two, as in the Armstrong guns. The mortar is placed in a hole, dug in the ground, a few inches left standing out; the earth is shovelled in, and driven down firm; a penthouse lid, to keep out rain, dirt, and insects, renders it complete. Amateurs require nothing of this kind. A small mortar may be a tube, open at both ends, and fitted with a wooden bottom, to which it is to be firmly screwed. Fig. 94 represents such mortar: it may be 4 diameters high; and the foot should have a conical hole turned in it to receive the cone fastened to the shell. The match is lit at t; but this may have a long bit of touch-paper attached to it, if preferred.

Instead of making a plaster mould, to form the shells in, the shells may be made by covering a wooden sphere, with paper, on the outside; when dry, they may be cut round in the lathe (a cross mark, with a pencil, having previously been made, as a guide to bring the same parts together again); the wooden mould removed; the cut edges glued; and the shell fitted up, in the usual way. Clean oil flasks may be covered with six or eight thicknesses of paper: paste an inch, or two, round the neck; when dry, cut through the cover, near the spherical part; file a notch all round, and snap it off. I have made excellent shells this way; the chief objection against them is their limited size. Glass globes might be blown, of uniform size, in moulds, like bottles. Another ready way of making shells, is to cover the india-rubber air-balls, of the toyshops, almost as thin as soap-bubbles; when the cover is dry, a hole may be cut, for the fuse, with a penknife, and they are ready, at once, to receive the stars. Their shape is that of a prolate spheroid, fig. 106. After eight thicknesses, or more, of paper have been pasted on, measure, with a tape, round the equatorial circumference, b e d, which suppose 17 inches; add 1 to this=18 inches. Measure from the pole, a, down the meridian by e to the opposite pole c, suppose 11 inches. Cut a piece of double-crown, 18 by 11; fold it down the middle, to a double thickness of 9 by 11; fold-again to 4¹/₂ by 11; again to 2¹/₄ by 11; there will, now, be eight thicknesses. Pencil the shape fig. 107 upon the top, and cut through the whole. Paste the eight gores on, as in fig. 106; for ornament, half may be pink; half, green. If these air-balls could be blown in a spherical mould, of uniform size, they would obviate the gluing process, which is, at present, a tedious and necessary evil; they would, also, be much cheaper, as they could be supplied for about 4d. per dozen, and save the cost of a great deal of needless labour.