20,366. Parsons, Sir C. A., Walker, R. J., Cook, S. S., and Simon, R. A. Sept. 30. Plant driving and transmission mechanism, special applications of; regulating.-In marine turbine installations, special or additional toothed transmission gearing is employed to maintain the speed of the main turbines at low powers, in combination with means for maintaining an efficient range of expansion in the turbines. In all the modifications described, toothed gearing is provided so that the ratio of the revolutions of a main turbine to the revolutions of the propeller it drives differs at low powers from the ratio at full powers. A single propeller-shaft installation, Fig. 1, comprises high and low pressure turbines a, b, both driving through toothed gearing g, f at high powers, while for low powers a second set of toothed gearing h, e is provided having a greater reduction ratio than the first. Suitable clutches c', c<2>, c<3>, c<4>, m, n are provided. An astern turbine c may be incorporated in the low-pressure turbine b, and a cruising stage k in the high-pressure turbine a, steam under cruising conditions being admitted by a pipe l to the stage k and passing through the turbines a, b in succession to the condenser. In a modification having two propeller shafts, each shaft has sets of turbines similar to those shown in Fig. 1, but each set has, in addition, cruising turbines operating the propeller shafts through double reduction gearing, the cruising turbines being geared to pinions on the shafts of the low-pressure turbines. Fig. 4 illustrates a three-shaft installation in which the wing shafts d<1>, d<3> are fitted with turbine sets as in the form shown in Fig. 1, while the middle shaft d<2> has high and low pressure turbines which only operate at high powers, a cruising . turbine o driving the shaft d<2> at low powers through double reduction gearing. The turbine o may exhaust (a) into the wing highpressure turbines a, whence the steam passes through the wing low-pressure turbines b to the condenser, or (b) into the wing turbines b while auxiliary exhaust steam is led by conduits s to the wing turbines a. The turbines and gearing of the middle shaft may be used on the wing shafts, and vice versa. In a further modification, Fig. 7, the main turbine set is provided with impulse-wheels only which are operative at all powers, the nozzle groups 1, 2 being both open for full power, while, for lower powers, gate valves are used to regulate the number of jets of group 2. The correct proportion of opening at each stage is determined by the relative sizes of pinions 3 engaging the racks 4 of the gate valves 5 or by the proportion of the bevel driving-gears which operate the pinions 3 from a single hand-controlled member. Only some of the initial stages may be regulated in this manner, succeeding stages being either of the impulse or reaction type or of a combination of these types. The stages may be of any suitable form of partial impingement type, such as are described in Specifications 28.047/07, 17,872/08, 27,907/08, 28,373/08, 28,375/08, 28,376/08, 27,283/09, 29,119/09, 2295/10, and 22,969/10. ln place of the ordinary cruising stages, coacting nozzle sections and reaction cruising stages as described in Specification 8980/11 may be used. Between the clutch-operating mechanism and the steam-supply valves to the turbines or stages, interlocking-gear, such as is described in Specification 804/13, may be provided to prevent the valves from being opened until the clutches are in the correct working position.