[548]. Is a modification of [547]. The pinion A may be controlled in speed by any hand or automatic device, to vary the speed of the driven pinion B. The belt pulley C carries round the bevil wheel D, driving B at a speed varying with the motion given to A.

[549]. Two wheels (one of which has a different number of teeth to the other) gearing into one pinion; used for counters and slow motions of all kinds.

[550]. Is an application of [No. 549] by internal or epicycloidal gear to pulley blocks. Moore’s patent ([No. 1545]) and Pickering’s patent are examples. The arm shown is not required where two internal loose wheels are used with different numbers of teeth, and one pinion as in [No. 1545], but if used is fixed to the pinion so that it is prevented from revolving, but retains its circular swaying motion; in this case, one internal wheel is movable and the other fixed, the speed being equal to the difference in number of teeth of the loose wheel and pinion at each revolution of the eccentric shaft.

[551]. Weston’s differential pulley block, consisting of a two-grooved pitched chain-sheave having different numbers of teeth, in combination with a return block and endless chain.

[552]. Differential screws. These may be both of the same hand, or one right and one left-handed, and any fractional speed secured by proportioning the pitches.

[Larger plate.]

[553]. Two-speed gear, operated by a double clutch, which throws either pair into gear as required.

[554]. Stewarts’ differential gear. Two cranks, one fixed to a sleeve and the other to a centre shaft, are driven round at varying velocities by a slotted crosshead revolving with the driving shaft. The two shafts are not in the same line.

[555]. Differential hydraulic accumulator. The effective area of the ram is the annular shoulder, or the difference between the areas of the top and the bottom rams.