The lifting charge projects the shell into the air and the time fuse, which is arranged to burn through at the top of the shell’s flight, ignites the bursting charge which opens the shell and fires the contents. The modern varieties of shell are almost infinite. Colours have been brought to a wonderful pitch of depth and brilliance, besides various kinds of fire for stars, producing stars with tails of the same and contrasting colours. Another class of shell, which might be called the compound, consists of shell filled with fireworks of other kinds—Roman candles, tourbillions, wheel-turning cases, small shell, and what gives undoubtedly the most dramatic aerial effect yet devised, with rockets. The “thunderbolt,” a shell 16 inches in diameter, containing a hundred 4-ounce rockets, has always been a popular feature of the Crystal Palace displays. Another variation of the shell is the comet, which is in effect a small shell (generally about three inches) with an exaggerated fuse of brilliant fire, which leaves a heavy tail during the comet’s flight. These are usually fired from either side of the firing-ground in rapid succession, producing an aerial arch, and opening just after having passed each other. The aerial maroon consists of a maroon fitted with a lifting charge and time fuse. CHAPTER III SIMPLE FIREWORKS—MINE CLASS The next group of fireworks is what may be called the “Mine” class, and has some of its members amongst the earliest firework units. To-day a mine consists of a quantity of small effects such as stars, crackers, squibs, etc., blown simultaneously from a case, or in display work—from a mortar. In the latter event they are made up into bags with the lifting charge below, and are known technically as “bags.” The “Mine of Serpents” and “Jack-in-the-Box” as sold in the shops consist of a rolled paper case which acts as the mortar, at the bottom of which is a lifting charge. This case has a light strawboard cover with a central hole, through which passes a case charged with a golden fountain composition, the lower end of which is not—as is generally the case—“clayed.” The space round the central case is filled in with squibs or crackers. When lighted the fountain case functions in the usual way, but when finished ignites the lifting charge, which lights and blows up the contained fireworks.