3922. Thomson, D., and Smith, W. Feb. 16. Movable-abutment type of explosion engines having rotary abutments. A driving - wheel has a channelled rim 2 divided into compartments b y partitions 3 which act as pistons for the motive fluid, and is surrounded by an annular water-jacketed casing 4 making tight joint at the packing rings 55. Each rotary abutment 11 containing admission and exhaust ports and valves is locked in position, except when a piston 3 has to pass, by a U- shaped piece 54, which is withdrawn at the right moment by a bell -crank lever actuated by a roller 51 running in a cam-track on a flange of the rotating wheel. Striking plates 34 or enlarged ends are fitted to the abutment arms, and plate springs 35 to the ends of the pistons. The spokes of the wheel carry racks 17, 18, 19 gearing with pinions 21, 22, 23 which may be clutched to the spindle 20, and pinions 24, 25, 26 which may be clutched to the spindle 27. These spindles drive the oil pumps 15, the air-compressors 13, and the valve-actuating cam-disks 47, one of each of these being provided for each abutment 11. The cut off and reversing valve consists of a hollow tube 36, passing through the centre of the abutment 11 and reciprocated in the end connexions 70, 74 by linkwork, acting at the collars 46 and actuated by the cam-disk 47. A partition 39 separates the admission and exhaust sides. Oil from the pump 15 is led by pipes 68, 53 to a nozzle at the partition 39, where it is sprayed into air coming from the compressor 13 through a pipe 73 containing a check valve 72. When the admission port 37 registers with a port 40 between the arms of the rotary abutment 11, the mixture passes to a chamber, sty 79, in the wheel, is exploded by a spark from the plug 57, and drives the wheel. The spent gas passes through ports 41, 38 to an exhaust pipe 75 on reaching the next abutment, and heats the incoming oil in the pipe 53. The explosions at the abutments occur one after the other ; admission to chamber 79 takes place while the exploded gases in chamber 80 are expanding. An explosion occurs in each chamber formed by the partitions 3 when the spindles 27, 20 are driven from the outer rack 17 ; one occurs in every other chamber when the spindles are driven at middle speed from the rack 18 ; and one in every third chamber when the drive is from the rack 19. To reverse the engine, each tubular valve 36 is turned through a right-angle by simultaneously actuated levers 48, so that the combustible mixture passes by ports 37 to the chambers 85, 81 instead of to the chambers 79, 80. The sparking-plugs 58 are then used. The reversing- levers also reverses the valves 59 of the watercooled compressors 13. These compressors, as well as the oil pumps 15 and the pump 16 for circulating the cooling-water in the water jackets, are all pumps of the rotary-abutment type constructed on the same principle as the engine itself. The engine may be arranged to rotate in one direction only in an horizontal plane, the spindles 20, 27 being connected to form the power shaft. The pinions 24, 25, 26 are used to give the three speeds forward, and the pinions 21, 22, 23 the reverse speeds. With suitable modifications, the machine may be used with steam or compressed air, or water, or as a pump.