“[The screw machine] was on the principle of the gauge or sliding lathe now in every workshop throughout the world; the perfection of which consists in that most faithful agent gravity, making the joint, and that almighty perfect number three, which is in harmony itself. I was young when I learned that principle. I had never seen my grandmother putting a chip under a three-legged milking-stool; but she always had to put a chip under a four-legged table, to keep it steady. I cut screws of all dimensions by this machine, and did them perfectly. (1846)”