f r h p K g - a b - m n - c o - S. Necessity in this case requires three springs, of which the first attends to the revolution of the wheel, the second to pushing the stone against that wheel, the third to keying the said wheel, and so on. Of the way of giving force to the wheel. Out of p, the pole (axle) of the wheel, comes the square front of this pole, which enters into the square concavity, made like the bezel of a ring, which has a diameter equal to the wheel that is set upon this pole; and around this pole the chain drawn here is wound with one complete turn. And this chain is pulled behind the screw-shaped spring, wound about the pole and joined to that chain, and the end of this spring rests at q and is always fixed there. And the wheel is keyed with the tooth r, which sticks into the lip of the wheel; and when it is released by pushing f toward h, the tooth r comes out of the lip of the wheel and, touching the side h, the wheel turns with fury and rubs against the fire-stone (flint) placed at g with one complete turn, and makes much fire, with which the powder in the receptacle K is lit. Of the three springs mentioned above, the first is the spring of power, which is made like a screw, wound about the column; and this it is, and fixed at q, and it is on the opposite side at the end of the column S. The second spring is the bc, which pushes the heel a and holds the tooth r fixed in the concavity that the above-said lip of the wheel has. The third spring is the mo; and this, pushing the heel n, keeps the stone g pressed upon the edge of the wheel that passes into the receptacle of the powder at K, and so on.

a - b. The wheel is keyed with the tooth a, which enters into the concavity b.