be a tin barrel; then this leader, being met by another brought from the end of the last case of the horizontal wheel, will give fire to the vertical wheel, as soon as the cones are extinguished; but the sun D must not be fired, till the vertical wheel is quite burnt out. Of Fire Pumps. Cases for fire pumps, are made in the same manner as those for tourbillons, only they are parted instead of being rolled dry. Having rolled and dryed your cases, fill them in the following manner: first put in a little meal powder, and then a star, on which ram lightly a ladle or two of composition, then a little meal powder, and on that a star, then again composition, and so on till you have filled the case. Stars for fire pumps should not be round, but must be made either square, or flat and circular, with a hole through the middle; the quantity of powder for throwing the stars must increase as you come near the top of the case, for if much powder be put at the bottom, it will burst the case. The stars must differ in size, in this manner; let the star which you put in first, be about one fourth less than the bore of the case, but let the next star be a little larger, and the third star a little larger than the second, and so on; let them increase in diameter, till within two of the top of the case, which two must fit in tight. As the loading of fire pumps is somewhat difficult, it will be necessary to make two or three trials, before you depend on their performance: when you fill a number of pumps, take care not to put in each an equal quantity of charge between the stars, so that when they are fired they may not throw up too many stars together. Cases for fire pumps should be made very strong, and rolled on four or eight ounce formers, ten or twelve inches in length each. Of the Vertical Scroll Wheel. This wheel may be made of any diameter, but must be constructed as shewn by fig. 57, to do which proceed thus; have a block made of a moderate size, into which fix four flat spokes, and on them fix a flat circular fell of wood; round the front of this fell place port-fires; then on the front of the spokes form a scrole, either with a hoop or strong iron wire; on this scrole tie cases of brilliant fire, in proportion to the wheel, head to tail, as in the figure; when you fire this wheel, light the first case near the fell; then, as the cases fire successively, you will see the circle of fire gradually diminish; but whether the illuminations on the fell begin with the scrole or not, is immaterial, that being left intirely to the maker. N. B. This wheel may be put in the front of a regulated piece, or fired by itself, occasionally. Of Pin Wheels.