Slinky

The Slinky is a helical spring toy invented in 1943 by American naval engineer Richard T. James, who noticed a torsion spring stepping downward after it fell from a shelf and set out to build a toy that could repeat the motion. Richard and his wife Betty James formed James Industries and began manufacturing the toy in Clifton Heights, Pennsylvania, selling each coil, 2 and a half inches tall and made of 98 coils of Swedish steel, for one dollar. The toy's breakthrough came on November 27, 1945, when the couple were permitted to demonstrate it on an inclined plane at Gimbels department store in Philadelphia, selling its first 400 units in 90 minutes, and it was introduced nationally at the American Toy Fair in 1946. Its ability to walk down stairs end over end and to appear briefly to float after being dropped made it a lasting success, with roughly 300 million sold in its first 60 years. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/