Fig. 118. A pyramidical piece: a scroll wheel in the middle; five horizontal wheels, or triangulars, at intervals, as represented by the rings; brilliant fixed cases playing obliquely upwards: at the bottom may be a row of cases playing downwards; these form what is called a cascade. Gerbes make the most effective cascades, but they require to be placed at a great height from the ground, if containing iron: the coke grains will be found suited for 8 or 10 feet.
Fig. 119. A spiral wheel: six cases on a horizontal wheel; lances arranged in a spiral, on cane, or hooping.
Fig. 120. A true-lover's-knot: six 6⁄8 wheel cases, playing in pairs; three saxons, one carrying a blue; one, a green; one, a crimson colour. Light at a; this leader blows across, and lights the opposite starting case. The tail of this case lights the saxons: the ends of the saxons at c, c, c, before enveloping them, are to be smeared with meal; the end, b, is also to be smeared with wetted meal, to insure the ignition of the leader. This is a most beautiful piece: the colours, on the saxons, form loops, and represent, in a slight degree, the compound motions of the moon and planets, with regard to the earth. The centres of the saxons are carried round in a circle, like the earth in her orbit; the colours on the saxons revolve round the flying centres, like the moon round the earth. The wheel must not be less than 3 feet diameter.
Fig. 121. A revolving globe. This is, also, a most beautiful piece. The bottom is a horizontal wheel, carrying a strong half hoop, a b c; a skeleton globe, formed with hoops, is suspended in this. This globe is driven by cases placed upon it, round a hoop, crossing the other hoops, at right angles, like the equator, at right angles to the meridians. The meridional hoops are covered with lances, white or coloured. The globe revolves vertically, while the wheel below turns it horizontally; the compound motion produces a peculiar oblique tumbling convolution, exceedingly perplexing to spectators, ignorant of its construction. Instead of a globe, the top piece may be a revolving cylinder.
Fig. 122. A mine. This is a cylindrical case, containing serpents. The bottom of the mine should be a circular piece of wood, glued in. On it, place a circular bag, containing F grain powder. The bag is made with two circular pieces of paper, one half-an-inch diameter larger than the other; lay the small one on the top of the large one: paste, or gum, the exposed rim of the bottom piece, and bend it up, and press it down on the small or top piece, all round, leaving a part through which to put the powder; when dry, put in the powder, and stop up the hole. Put it into the mine, smear it with the brush, dipped into meal paste, in the usual way; and, with a pepper-box, shake in a little dry meal. Take a fixed case, charged; envelop it, so that the paper projects about an inch at the bottom: take a piece of squib-case, the same length as the serpents; put through it a piece of match, long enough to protrude at the top, half-an-inch, and to bend over, to form a hook: tie this in the envelope of the fixed case. Fill the mine with serpents, naked primed mouth downwards: with the scissors, or a pair of pliers, draw out the middle serpent; put in the matched squib-case; hold the fixed case upright, in the mine, and ram pieces of torn paper tight round it, to offer resistance, and cause the serpents to be blown higher. To adjust the blowing powder in the bag, use the following formula, I denoting the diameter in inches.
I x 2I = drams.
Required the quantity of powder for a mine 11⁄2 inch diameter.
11⁄2 x 3 = 41⁄2 drams = 1⁄4 oz.
For 13⁄4 inches?—13⁄4 x 31⁄2 = 7⁄4 x 7⁄2 = 49⁄8 = 61⁄8 drams = 3⁄8 oz.
For 2 inches?—2 x 4 = 8 drams = 1⁄2 oz.