Barry Allen built the Cosmic Treadmill so that he could travel through time by use of super-speed. It was powered by cosmic rays and was coordinated with radioactive pulses from a cosmic ray clock. It released positive radiation when moving forward, sending its user into the future, and negative radiation when moving forward, sending its user into the past.
Near the end of its construction, Barry had only one bug to fix. The positive radiation which sent him into the future caused an electro-magnetic reaction in his body, charging him with positive ions and making him a living magnet.
Barry used the Cosmic Treadmill in many of his exploits. He needed only to program what year he went to and jump on. He had to keep an internal vibration while in the new time period. As soon as he wanted to return to the 20th century, he just released the internal vibrations and he was home.
He used it to travel to the 25th century to save the future from an atomic clock that had been sent there in a time capsule and was going to turn into an atomic bomb. On this trip, he had his first encounter with Professor Zoom.
Before the Crisis on Infinite Earths, it could also be used to travel to other universes. After Barry's disappearance during Crisis, Jay Garrick and Wally West, along with the Earth-One and Earth-Two Supermen, used the treadmill to travel to Earth-Two, only to find a black void. Wally noted that it was destroyed beyond repair after that trip. However, that must not have been the case, since it appeared in later stories.
The cosmic treadmill eventually came into the possession of the Flash Museum. It was instrumental in Wally's defeat of Professor Zoom in the Museum. Wally threatened to use it to visit Zoom as a young man in the future to torment him or just kill him in his crib. Wally set the controls for Zoom's era, began to run, and jumped off so fast that Zoom didn't see him. Thinking that Wally had really gone to the future, Zoom chased after him, only to be sent to his home century, defeated.
After Jenni Ognats, XS of the Legion of Super-Heroes, had been stranded in the 20th Century, she was trying to find a way to return to her friends. It just so happened that another time traveller, John Fox, Flash of the 27th century, was also in town at the time. He, using technology from his own suit, reconfigured the treadmill so that Jenni would not have to keep internal vibrations to remain in the 30th century.
The treadmill eventually wound up in an antique shop in the 25th century. There, it was stolen by Eobard Thawne, who used it to travel back to the 20th century and pose as Barry Allen.
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