The Gimbels department store is gone, the Cramp Shipyard long gone, but the Slinky slinks on.

The short stack of flat, coiled metal - created at one Philadelphia landmark and first promoted and sold at the other - turns 70 this year, an accidental toy that has become standard equipment for childhood and an enduring part of the culture.

"It's magic," said Tod Corlett, director of industrial-design programs at Philadelphia University, and who still owns his boyhood Slinky. "It's sensual and visceral and pure."

The Slinky prospers despite - or because of - being a low-tech toy.

It has no flashing lights, requires no computer link or electrical outlet. It doesn't need batteries.

Its power is its simplicity, a spiral too slack to be a spring but perfect for flipping head over tail to "walk" down a flight of stairs - or to stroll to infinity on escalators and treadmills.

It's portable, appeals to both sexes and to all ages, still made at a factory in the central Pennsylvania borough of Hollidaysburg. It has survived changing tastes - and the odd end of its inventor - to travel the globe and beyond.

The Slinky has walked on the Great Wall of China, blasted into space aboard the shuttle Discovery, and jiggled across movie screens in the form of "Slinky Dog," the Toy Story dachshund with the Southern accent.

"It's an international toy, an international language," said Bob Swaim, a retired Souderton High School math teacher who wants the Slinky to be designated the official state toy of Pennsylvania.

How many Slinkys have been sold?

Estimates go as high as 350 million worldwide. Alex Brands, the third company to own and produce the Slinky, said it has no way to confirm that number. The private firm, based in Fairfield, N.J., does not release current sales figures.

"It still does really well for us," spokeswoman Sally Lawrence said.

Today, a plain-box Slinky costs $4.99, but buyers don't have to settle for steel - a 14k-gold-plated version sells for $149.99.

The 70th anniversary will pass without a cake. Instead, Alex Brands has asked Slinkyphiles to post online videos of themselves singing the advertising jingle.

When people post with hashtag #SlinkyDay70, the firm donates Slinkys to Toys for Tots, the Christmas-time charity for needy children.

An unexpected invention

Richard James never planned to invent the Slinky, but he knew a great idea when he saw one.

In 1943, four years after earning a mechanical engineering degree from Pennsylvania State University, he was working at the Cramp Shipbuilding Co. on the Delaware River. He sought to devise a spring that could keep sensitive shipboard equipment stable despite the rise and fall of the ocean.

James had experimented with hundreds of coils when a reject fell off a shelf - some accounts have it tumbling from his desk - and flounced around the floor. He took the coil home to his son, who got it to walk down stairs.

For the next two years, James experimented with metals and proportions, finding that a tensionless ribbon worked best.

He asked his wife, Betty, to name the thing. She looked through a dictionary and picked "slinky" - meaning graceful and sinuous in movement.

James had a Philadelphia piston ring firm produce about 450 Slinkys, but toy companies didn't rush to buy.

The big break came in 1945, when Gimbels agreed to try it out during the Christmas rush.

On the evening of Nov. 27, James showed quizzical shoppers how the Slinky could walk down an incline, and the craze began. His stock of 400, priced at $1 each, sold out in 90 minutes.

He and Betty rented factory space in Germantown. Soon the new James Industries had six machines turning out 100 Slinkys an hour.

"Strictly speaking, I didn't invent Slinky," James told a newspaper in 1948. "He practically walked into my life."

Trouble lay ahead. In 1960, as the Slinky company struggled with debt, James called his family together in the kitchen of their Main Line estate.

"I'm going to Bolivia," he announced. "Who wants to go with me?"

The answer: no one.

James left his wife, six children age 2 to 18, and the business to join an evangelical group, the Wycliffe Bible Translators, in South America. He would die there in 1974.

"These religious people always had their hands out," Betty James told the New York Times in 1996. "He had given so much away that I was almost bankrupt."

In 1963, running the company alone, Betty James mortgaged her house to make a big push for Slinky at the New York toy show - successfully attracting new orders and attention.

A rare female CEO in that era, she moved the company forward, embracing national advertising. By the mid-1960s, many children knew the Slinky jingle by heart:

What walks down stairs alone or in pairs and makes a slinkety sound? A spring a spring, a marvelous thing. Everyone knows it's Slinky.

Betty James expanded the line, adding Slinky Junior, plastic versions, and rainbow colors. She quickly agreed to Slinky Dog's inclusion in the 1995 Toy Story movie, which brought new fans and sales.

Over time, she made sure the Slinky stayed affordable - and stayed a Slinky, not becoming something else.

In 1998, after nearly 40 years as CEO, she sold the company to Poof Products. Last year that firm and two others merged to become Alex Brands. Betty James died in Philadelphia at age 90 in 2008.

The scholarly Slinky

University scholars have used the Slinky in studies of biped locomotion - that is, walking. Physicists love it for its reactions to gravity. Math teachers use it to teach about equilibrium, mass and diameter.

"There's so much discovery you can do with a Slinky," said Swaim, who owns 40 different models.

The U.S. Postal Service gave the Slinky its own stamp. The Smithsonian put a Slinky on display, beside Kermit the Frog and Dorothy's ruby slippers from The Wizard of Oz.

Corlett, of Philadelphia University, keeps his childhood Slinky in a red wooden box he built with his father.

"There's something addictive about how a Slinky feels and sounds when tossed from one hand to another," he said. "It looks like fine jewelry, or like the laboratory equipment it originally was."