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The teeth are set to engage in those of the spur-wheel, one band on each side, so that the effective stroke in one case is downward, while in the other it is upward. These toothed bands are drawn together at their lower ends by a spring, and they are also kept under downward tension by weights or a powerful spring beneath.
In this way the machine is so arranged that, no matter at what point the stroke imparted by the movement of the buoy may be arrested, there is always one or other of the ratchets or of the teeth which will fall into engagement with the tooth of the spur-wheel, very close to its effective face, and thus the momentum acquired by the one part before it impinges upon the other becomes comparatively small.
The limit to which it may be practicable to multiply ratchets or toothed bands will, of course, depend upon the thickness of the spur-wheel, and when this latter has been greatly enlarged, with the object of providing for this feature, it becomes virtually a steel drum having bevelled steps accurately cut longitudinally upon its periphery.
Perhaps the most convenient development of the system is that in which the spur-wheel is driven by two vertically pendant toothed bands, resembling saws, and of sufficient length to provide for the greatest possible amplitude of movement that could be imparted to them by the motion of the buoy.
The drum may carry a crank and shaft, which works the spur-wheel and toothed bands as already described, so that no matter at what stage in the revolution of the drum an upward or downward stroke may be stopped, the motion will still be communicated in a continuous rotary form to the fly-wheel.
Every rise and fall in the pressure of the water now effects a movement of the spur-wheel, and the latter may conveniently be connected with the strong spring of a clockwork attachment, so that the water pressure is really used for winding up a clockwork ventilating-fan.
A small spur-wheel is gripped on two sides by two metal laths, with edges serrated like those of saws, and held against the wheel by gentle pressure.
Each of the bottom rolls carries at its end a large spur-wheel, these spur-wheels, which are on opposite sides of the machine, each gearing into a pinion on a shaft which runs from end to end below the rolls, and which is itself geared to the shaft carrying the belt pulleys, as shown. This is a very simple and direct mode of driving, and avoids the necessity for small wheels on the rolls.
Each, however, must be set to catch the teeth of its own separate spur-wheel; and, inasmuch as the direction of the motion in one case is different from what it is in the other, it is necessary that, by means of an intervening toothed wheel, the motion of one of these should be reversed before it is communicated to the fly-wheel.
The shock occasioned by the blow of the ratchet on the spur-wheel, or of one tooth upon another, may be reduced almost to vanishing point by multiplying the number of ratchets or toothed bands, and placing the effective ends, which engage in the teeth of the wheel successively, one very slightly in advance of the other.
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