tubes, thereby dispensing with the short flues leading into the smoke chamber, as well as with the curved flue last described. Figures 1 and 2, sheet 4, shows the lower part of fire box for a locomotive boiler, made like the ordinary marine boiler, thereby dispensing with the usual ash pan, and admitting a simple mode of making a water grate, by introducing tubes lengthwise or crosswise of the fire box, filled with water and connecting the opposite water spaces of the fire box. In this arrangement, it is intended to put the boiler together with screw bolts, that the back fire box may be easily removed, after which, by removing the stays and short tubes in front, the whole interior fire box may be taken out for repairs. Figures 2, 3, and 6, show the same arrangement of steam pipe, as is shown in the drawings for the marine boiler. Sheet 7 shows an arrangement of boiler, suited to the present form of locomotives generally, similar to the arrangement shown on sheet No. 3, with the single difference of passing a portion of the flame or combustible gases through the tubes containing water, by means of the tubes with the bent ends connecting with the back plate of furnace, and leading from thence into the smoke chamber. Sheet 8 shows another modification of the locomotive boiler. In this instance, the fire box is extended into the forward part of the boiler without interruption, until it reaches the smoke chamber, making a clear open space, or single flue, half round at the top, straight sides and bottom, with rounded corners. To obtain the necessary amount of fire surface in this boiler, the whole interior surface is studded at regular intervals, with tubular stays of such length and diameter as may be found most convenient, and so distributed as to bring the greatest amount of surface in contact with the flame or heated vapor, previous to its reaching the smoke chamber. It is intended to put this boiler also together in such a manner with bolts, as will enable it to be taken apart without difficulty, after taking out the tubular stays. Sheet 6, figures 1, 2, 3, 4, and 5, shows a slight modification in the mode of arranging the water pipes in the interior of a locomotive boiler. In this case, the tubes or pipes containing water, are made much larger than in any previously described; and by inspection of the drawing, it will be seen that the mode of attaching the ends of the tubes is slightly different, which, instead of passing from end to end of fire box, are in some cases attached to cross pipes in the fire box, and in others are bent at right angles, and attached to cylindrical part of fire box. Sheet 6, figure 1, shows a mode of putting in the inside flue so as to take the flame at any point of the tube containing water that may be deemed most advisable. A small tube, flattened on one side, is put across the tube containing water, into which the cross tubes are fixed, the smaller flue leading to smoke box. Sheet 6, figure 5, shows an arrangement for introducing atmospheric air into the fire box, and for heating it before it is allowed to mix with the combustible gases evolved from the fire; two or more pipes of cast or wrought iron, or of fire clay if necessary, are placed within the fire box, as shown in section. At figure 4, sheet 6, extending forwards to the tube sheet, fitting closely to the tubes that come opposite to them; pipes are fitted to the tubes leading through the smoke box to the external air, which are furnished with funnel shaped mouths, so that the forward motion of the engine, as well as the vacuum caused by the escape steam,