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 1 inch, only 1 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 2 ounces of F grain, according to the fit in the mortar. The hole, in the wooden fuse, should be 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 × 1 = 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, 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= 3d3. 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 8 inches diameter, and 16 inches long.

The same computation is more readily effected by multiplying the diameter by ; V} = V1⁄2 = } 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

K

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 screwchuck, 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.

ASTEROID ROCKETS.

These differ from other rockets only in the head, which contains a parachute for floating a coloured case, attached to the strings. The parachute is best formed of silk, or alpaca; it may also be made of black glazed lining, or of tissue paper, carefully rubbed, till the stiffness is removed. The colour should be dark, that it may be invisible. If of silk, or alpaca, the parachute may be 20 inches square, with 4 strings attached to the corners; or it may be made of 6 triangular pieces, sewed together, like an umbrella. If of tissue paper,

the paper may be of a circle, or of an octa