The Slinky Began as a Ship Spring That Fell Off a Shelf

Set a Slinky on the top stair, tip its upper end over the edge, and it pours itself down to the next step, gathers, and tips again, all the way to the hall floor with a soft metallic whisper. It looks like a toy somebody must have dreamed up on purpose. It was really a piece of ship's equipment that fell off a shelf.

A spring with a serious job

In 1943 a mechanical engineer near Philadelphia was working on a set of springs meant to hold sensitive instruments steady on board ships, even in rough seas. According to the Lemelson-MIT Program he knocked one of his springs off a shelf by accident. It did not flop into a heap. It stepped, in a series of arcs, from the shelf to a stack of books, to a tabletop, to the floor, where it gathered itself back into a coil and stood upright.

He tried it again and again, and the spring kept walking, down stairs as well. It was his wife who saw that the thing was a plaything and not a failed ship part. She also gave it its name: The Strong National Museum of Play says she searched the dictionary and came back with the word slinky.

From shelf to shop counter

The couple borrowed 500 dollars to get started, and the engineer built a machine that could coil 80 feet of steel wire, about 24 metres, into a finished Slinky in roughly ten seconds. Sales were slow at first. Then, for Christmas 1945, the Gimbels department store in Philadelphia let them demonstrate it to shoppers. Lemelson-MIT records that 400 were sold in 90 minutes; the museum says simply that the first 400 went within minutes. Either way, the spring had found its real job.

A patent followed, granted on 28 January 1947 under the modest title Toy and Process of Use. By the toy's fiftieth birthday in 1995, more than 250 million had been sold around the world, and in 2000 it was given a place in the National Toy Hall of Fame. Along the way it wandered back into serious work: teachers use it to show how waves travel, and NASA took Slinkys aboard the Space Shuttle for physics experiments in weightlessness.

1. 1943 A spring meant for ship instruments falls off a shelf and walks
2. 1945 Shown to shoppers at Gimbels in Philadelphia, where the first 400 are sold
3. 28 January 1947 The patent, Toy and Process of Use, is granted
4. 1995 More than 250 million sold by the fiftieth birthday
5. 2000 A place in the National Toy Hall of Fame

What people often get wrong

Many people assume the Slinky was invented as a toy, by a toy company. It was a by-product of engineering for ships, and it took a second pair of eyes to see what it was for. The other common belief is that a Slinky will walk down any staircase, as it does on the screen. The museum that honours it admits otherwise: most household stairs turned out to be too tall and too wide for it, although it performed beautifully on television. If yours stalled halfway down, the fault was the stairs.

How the walk works

Nothing inside a Slinky pushes it along. The patent describes a spring wound so that its turns rest against each other without squeezing or pulling when it is left alone, and made of flat wire, wider than it is thick, which makes it unusually easy to bend. Tip the top over a step, and the turns flow across in a fan from the pile at the high end to a new pile at the low end. As the patent puts it, once started the spring carries on end over end down the steps with no further push, on gravity alone.

That is the whole trick: a first nudge, gravity, and a very relaxed piece of steel. An engineer set out to keep instruments still on a rolling ship and ended up with something that cannot keep still at all, which is a fine result for one clumsy moment at a shelf.