The Slinky was invented by accident

In 1943, mechanical engineer Richard James was designing a device that the Navy could use to secure equipment and shipments on ships while they rocked at sea. As the story goes, he dropped the coiled wires he was tinkering with on the ground and watched them tumble end-over-end across the floor.

After dropping the coil, he could have gotten up, frustrated, and chased after it without a second thought. But heas inventors often dohad a second thought: perhaps this would make a good toy.

As Jonathon Schifman reported for Popular Mechanics, Richard James went home and told his wife, Betty James, about his idea. In 1944, she scoured the dictionary for a fitting name, landing on slinky, which means sleek and sinuous in movement or outline. Together, with a $500 loan, they co-founded James Industries in 1945, the year the Slinky hit store shelves...

Seventy-two years ago, Richard James received a patent for the Slinky, describing a helical spring toy which will walk on an amusement platform such as an inclined plane or set of steps from a starting point to successive lower landing points without application of external force beyond the starting force and the action of gravity. He had worked out the ideal dimensions for the spring, 80-feet of wire into a two-inch spiral. (You can find an exact mathematical equation for the slinky in his patent materials.) It was Betty that masterminded the toys success.