Note, all the vents in the under side of the cases must be lighted at once; and the sharp point of the cone cut off, at which place make it spherical. To make Wheels and other Works incombustible. It being necessary, when your works are new, to paint them of some dark colour; therefore, if instead of which, you make use of the following composition, it will give them a good colour, and in a great measure prevent their taking fire so soon, as if painted. Take brick-dust, coal ashes, and iron filings, of each an equal quantity, and mix them together, with a double size, made hot. With this wash over your works, and when dry wash them over again; this will preserve the wood greatly against fire. Let the brick-dust, and ashes, be beat to a fine powder. Of Single Vertical Wheels. There are different sorts of vertical wheels, some having their fells of a circular form, others of an hexagon, octagon, or decagon form, or any number of sides, according to the length of the cases, you design for the wheel: your spokes being fixed in the nave, nail slips of tin, with their edges turned up, so as to form grooves for the cases to ly in, from the end of one spoke to another; then tie your cases in the grooves, head to tail, in the same manner as those on the horizontal water wheel, so that the cases successively taking fire from one another, will keep the wheel in an equal rotation. Two of these wheels are very often fired together, one on each side of a building, and both lighted at the same time, and all the cases filled alike, to make them keep time together, which they will do if made by the following directions. In all the cases of both wheels, except the first, on each wheel, drive two, or three ladles full of slow fire, in any part of the cases, but be carefull to ram the same quantity in each case, and in the end of one of the cases, on each wheel, you may ram one ladle full of dead fire composition, which must be very lightly drove; you may also make many changes of fire, by this method. Let the hole in the nave of the wheel be lined with brass, and made to turn on a smooth iron spindle. On the end of this spindle let there be a nut, to screw off and on; when you have put the wheel on the spindle, screw on the nut, which will keep the wheel from flying off. Let the mouth of the first case be a little raised. See fig. 39. Vertical wheels are made from ten inches to three feet diameter, and the size of the cases must differ accordingly; four ounce cases, will do for wheels, of fourteen, or sixteen inches diameter, which is the proportion generally used. The best wood for wheels of all sorts, is a light, and dry beech. Of Horizontal Wheels.