The Helical Spring Toy: A Spring Too Soft to Hurry

A helical spring that walks down stairs by itself, flowing its turns from one end to the other, looks like magic. It is careful proportion: flat wire, turns that just touch without pressing on each other, and a stiffness so low for its weight that every motion is slow enough to see. Richard T. James of Upper Darby, Pennsylvania, assignor to James Industries, filed US 2,415,012, *Toy and Process of Use*, on 21 August 1946; it was granted 28 January 1947. The patent sets out the proportions: a flat cross-section about four times as wide as it is thick, a coil diameter about thirty times that width, no compression between turns at rest, and a natural frequency between 10 and 100 cycles a minute. This rung works out why that combination walks, and measures a spring toy's stiffness and waves.