ENGINES, STEAM ROTARY. The Tower Spherical Engine.—The construction of this engine is described in detail, with illustrations, in Proc. limt. M. E., 1Ss5. Space will not admit of the complete description being given here, but the following abstract gives a clear idea of its geometrical principles. The spherical engine consists, as its name implies, of a system of parts contained within a sphere, and so united as to enable them under the action of steam-pressure to impart rotary motion to a shaft. It is an engine that seems peculiarly suitable for high-speed direct driving. It is the invention of 31r. Beauchamp Tower, to whom the idea of its construction originally occurred through watching the relative motions of the three parts composing a universal joint.
Geometrical Construction : Considered geometrically, the three elementary moving parts of which the engine is composed are, a pair of quarter-spheres _A and 13, with a circular disk P of infinitesimal thickness interposed between them, the diameter of the disk being the same as that of the sphere of which they are sectors. The sU•aight edges of the sectors are hinged on opposite sides of the disk along diameters at right angles to each other, as illustrated in the diagram, Fig. 1, in which the disk P, being seen edgewise, appears as a straight edge 0111y. E11.01 sector rotates upon an axis of its own, upon which it is fixed symmet : the two axes lie in the same plane, which is the plane of the paper in Fig. 1. and they meet in die eenter of the disk 1' at an angle of 135'. The two seetions-t and 11 thus eorrespond with the two LOWS of tom ill'flionry universal joint, and the disk I' answers to the cross-piece con neeting the bows, Starting from the position shown in Fig. 1, and supposing the direction of rotation to be such that the lower portion of the right-hand sector is approaching toward the eye while its upper portion is receding, as indicated by the arrows, the relative positions alter three successive eighths of a revolution will be as shown in Figs. 2, 3, 4.
Considering first the relative motions of the left-hand sector A and the disk P, it is seen that in Fig. 1 this sector is in close contact throughout with the lower half of the disk ; while
between the sector and the upper half of the disk there is a cavity equal to a quarter sphere. In rotating from Fig. 1 to Fig. 2. a cavity is opening between the sector A and the lower half of the disk P. while the upper cavity is closing to the same extent. In Fig. 3 the opening and closing cavities are of equal size, each being one-eighth of a sphere. In Fig. 4 the opening cavity has become still larger and the closing cavity still smaller ; and after t he next eighth of a revolu tion the opening cavity will be fully open and the closing cavity entirely closed, the relative positions thus being again as in Fig. 1, except that each sector is now reversed end for end, having completed half a revolution upon its axis. A similar opening and closing of cavities has been progressing simultaneously between the disk P and the right-hand sector B. Throughout each revolution there are consequently two cavities simultaneously in process of opening and two others in process of closing, all four alike at the same mean rate of increase and diminution. If, therefore, the disk with its pair of sectors be incased within a hollow sphere of the same diameter, and if steam be admitted into the two opening cavities and exhausted from the two that are closing, continuous rotary motion will be produced, driving the two shafts represented by the axis of the two sectors. When one of the two opening chambers is only just commencing to open, the other is half open ; so that while the one is making no effort the other is in the position of best effort, and the mean effort of the engine is as uniform as that of a two-cylinder engine with cranks at right angles. It is also evident, as an interesting feature in the system, that, although the whole of the engine may be said to be contained within the sphere itself, yet the capacity of the engine is no other than the full capacity of the sphere itself, inasmuch as foie• quarters of the sphere are filled and emptied in one revolution.