The effect of the diver is to give forth a light extremely brilliant and very white, and to plunge from time to time into the water, only to reappear with the same splendor. It is charged also with fires that gush forth to represent jets of water, or trees in blossom, which dive at intervals in the same manner. (Pl. VIII, fig. 6.)
The case has a length of 12 interior diameters. If the composition is a slow-burning one for illumination, the case is loaded upon a base from which issues a spindle having a diameter half that of the case. If a lively composition for forming jets is used, the spindle should have one-fourth of the same diameter.
For cases 10 lines in interior diameter, in which the throat has a quarter of the diameter of the opening, three charges of composition are first poured in, and this is followed by three-quarters of a gros of grain powder. If the throat has a semidiameter, the quantity, is 1 1/4 gros. An equal quantity of powder is added to each series of three charges of the composition. When the case has been loaded, it is closed with a pasteboard plug, and choked. The effect of this quantity of powder is to make the piece dive, by reason of the resistance which the sudden burning causes it to encounter in the air and the reaction within the case.
The case is lengthened by rolling on the lower end three or four turns of paper, which have a length sufficient to contain 4 1/2 ounces of sand, or of earth, which serve as a counterbalance. This is tied on the choke, after the sand has been placed within. It is closed tightly by a ligature.
Since this counterweight, of which the effect is to hold the firework on the water in a perpendicular position, would draw it to the bottom by its weight if it were not sustained on the water, the case is equipped to be thus sustained by gluing on, in place of the choke, a disk of pine pierced in the middle, into which it is forced. The diameter of this disk should be three of the exterior diameters of the case, and its thickness two-thirds of one diameter.
The case is primed and greased in the manner already described for the genouilleres.