Tempiscope

The tempiscope was the final invention of human scientist Mat Wyatt. It resembled an ordinary but was capable of showing events from the past, present and future. It was activated, like an ordinary kinetoscope, by dropping nickels into the device.

Foreseeing his murder at the hands of Jimmy Deparis, Wyatt had the tempiscope hidden in an arcade and told detective Elliot about its presence. After Wyatt was indeed murdered by Deparis over the plans for the bacterial spray, Elliott went to the arcade before Deparis and watched the future events on the tempiscope, thus learning that Deparis would soon come to the arcade himself. Deparis, trying to remain inconspicuous by casually patronising the arcade while the police expected a running fugitive, confused the tempiscope for an ordinary "nickelodeon" and watched in bafflement as the machine showed him the very events that had led him here before catching up to the present and showing him police officers Elliot and Sandy hot on his heels. Terrified, he tried to escape out a window and fell to his death. When Sandy asked Elliot how he knew to be there, Elliot showed him the tempiscope. These events became known to the Fourth Doctor as one of his "time tales". (COMIC: Dr. Who's Time Tales)