they cannot, therefore, need any description. When it is intended to use water for condensing instead of air, my improved steam-engine must be made as before directed, except that the communication between the air-vessel and the fire-place must be closed, which may be done by a perfect ring of iron surrounding the opening leading to the fire-place, instead of the half ring before described, and a forcing pump must be employed to draw water from a reservoir, and force it into the vessel which I have hereinbefore denominated the air-vessel, but which in this mode of working would more properly bear the name of water-vessel. In this case a blowing cylinder, the dimensions of which must be calculated according to the quality of the fuel to be used, may be worked to blow the fire through a pipe leading into the ash-pit. This, however, will not be necessary where there is a chimney high enough to create a strong draught. In respect to proportions, my improved steam-engine admits of considerable latitude, and it will be sufficient direction to any practical engineer to say that for engines working with steam of 120 lbs. to the inch, used expansively till it be nearly reduced to atmospheric strength and then condensed, a 10-horse engine may have a fire-place of 20 inches diameter, the flue at the top 10 inches diameter, and a boiler of 20 feet high; a 60-horse engine, a fire-place of 36 inches diameter, a flue of 16 inches diameter, and a boiler of 20 feet high. In boat-engines, and in other cases where height cannot be allowed, the diameter must be increased. The thickness of the two tubes constituting the boiler sides of a 10-horse engine may be 1/8th of an inch, that of a 60-horse a quarter of an inch, and so in proportion for engines of other power. The tubes constituting the condenser and inner tube of the air-vessel may in all cases be 1/8th of an inch thick. The outer tube may be 3/8ths of an inch thick, to afford stability to the working cylinder, the blowing cylinder, and the forcing pump fastened to this tube, and as an ultimate perfect barrier against explosion. The respective distances of the other tubes constituting the outside of the boiler, the condenser, and air-vessel, will be the same as hereinbefore given, and therefore their diameters will depend upon the diameter of the fire-place. The cap-piece in small engines may be half an inch thick, and in large engines an inch. The bottom of the ash-pit and bottom of the boiler must have about half an inch of thickness for every foot diameter, or they may be cast with ribs to afford equivalent strength. The fuel is supplied through a door in the flue, at the top of the boiler, consisting of coke or coals the least liable to swell with heat. The flue may be filled to about one-third of the height of the boiler, and the water fill about three-fourths of the boiler, leaving one-fourth for steam.