In the various composition of aquatic fire-works, although more care and attention are required, it is to be observed, that, in forming water-rockets, horizontal wheels, water-mines, fire-globes, water-balloons, water-squibs, water-fire-fountains, and the like, substances are generally used along with the usual ingredients, which, under particular circumstances, may be said to _repel_, as well as resist the action of the water; and in this particular they resemble the celebrated Greek fire, of which we shall speak hereafter. This remark, however, applies only to certain works. After the rockets have been filled, their ends are dipped in melted rosin or sealing-wax, or secured with grease. Fire-works, usually exhibited in rooms, are made with odoriferous gums and perfumes, and hence are called odoriferous fire-works. We may remark, that the odour or perfume is given by a variety of substances; for these, at a high temperature, are partly consumed, and partly evaporated. Thus camphor, yellow amber, flowers of benzoin, myrrh, frankincense, cedar-raspings, and the essential oils, particularly of bergamot, are employed for this purpose. Scented fire-works are of the same character. The Italians and the French, who have made more experiments in Pyrotechny, than other nations, have improved odoriferous fire-works. In these compositions, they also employ storax, calamite, gum benzoin, and other substances. _Scented fire_ was greatly in use in Egypt, Rome, and Athens, at their fetes and public ceremonies. The unpleasant smell which gunpowder, sulphur, &c. occasion in a confined apartment, has induced the modern artificers to add sundry odoriferous substances to their pyro-mixtures. On this subject, it will be sufficient to observe, that the _scented vase_, which was in use at Athens, contained the following substances: storax, benzoin, frankincense, camphor, gum juniper in grains, and charcoal of the willow. It does not appear that nitre was employed. The custom of burning frankincense before the altar, is indeed very ancient; for, in the primitive temple at Jerusalem, the custom was adopted by the priests in the Sanctum Sanctorum, and is continued by the Greeks and Armenians, the Jews, the Turks, the Persians, (especially the followers of Zoroaster), preserve this custom. The _Holy Fire_ of the latter is nothing more than the inflamed carburetted hydrogen gas, which comes from the naphtha ground at Baku.