Students of applied mechanics are agreed that ‘the technical advance which characterises specifically the modern age is that from reciprocating motions to rotary motions’, and the crank is the pre-supposition of that change. The appearance of the bit-and-brace in the 1420s and of the double compound crank and connecting-rod about 1430, marks the most significant single step in the late medieval revolution in machine design. With extraordinary rapidity these devices were absorbed into Europe’s technological thinking and used for the widest variety of operations. How can we explain the delay of so many centuries not only in the initial discovery of the simple crank but also in its wide application and elaboration?
Continuous rotary motion is typical of inorganic matter, whereas reciprocating motion is the sole form of movement found in living things. The crank connects these two kinds of motion; therefore we are organic find that crank motion does not come easily to us. The great physicist and philosopher Ernst Mach noticed that infants find crank motion hard to learn. Despite the rotary grindstone, even today razors are whetted rather than ground: we find rotary motion an impediment to the greatest sensitivity. The hurdy-gurdy soon went out of use as an instrument for serious music, leaving the reciprocating fiddle-bow – and introduction of the tenth century – to become the foundation of modern European musical development. To use a crank, our tendons and muscles must relate themselves to the motion of galaxies and electrons. From this inhuman adventure our race long recoiled.