Chronoscope

A chronoscope or time viewer is a device that uses images that show past or future events like a television. They can sometimes also cause time travel. They are common in sci-fi, and often take different forms.

Some act like cameras recording past and future events and showing what an object would look like in a different time period. Others are more like TVs and show videos and visions of the past and future. Chronoscopes are often used as plot devices, as they can often reveal various details that are necessary for the plot.

Compare Magic Mirror or Crystal Ball, which may have the ability to show these events as well.

Anime & Manga

 * Pokémon Lucario and The Mystery of Mew: When activated, the Time Flower shows visions of the history of a place.

Comic Books

 * In a Superboy comic story (based on a script from the Superboy live-action TV series that wasn't, apparently) Superboy flies out into space in order to make a home movie type film to show his friend that the friend's father was a hero during the war. Superboy goes faster than light so he can film the light coming from earth which shows what happened in the past.
 * Krona uses one to see the beginning of the universe (unknowingly altering it in the process) in the Green Lantern comics.

Films -- Live-Action

 * The scroll in Tim Burton's Alice in Wonderland that showed the history of Underland and then prophesied Alice's return and her slaying the Jabberwocky.
 * In the Denzel Washington movie Deja Vu, it's claimed that the "Snow White" technology is just an incredible complicated surveillance system. Turns out that its actually a chronoscope.

Literature

 * The Dead Past by Isaac Asimov is centered around such a device.
 * The first half of Pastwatch the Redemption of Christopher Columbus is all about this kind of device. Then they figure out how to do actual time travel...
 * "The Light of Other Days", by Arthur C Clarke and Stephen Baxter, has the WormCam.
 * The Time Machine stories by Donald and Keith Monroe. The title time machine had a viewing device that allows its users to see scenes of the future and past before traveling to them.
 * Discworld
 * On the Discworld, there are the Omni-scopes which have the power to do this, although true to form the wizards spend a great deal of time and effort trying to eliminate that capacity, treating it as a bug instead of a feature. It seems all they wanted was an expensive version of a webcam.
 * Also from The Science of Discworld books, Hex is able to treat our entire universe as one of these. Fast fowarding, or rewinding to see specific spots in human history (our universe canonically exists in a snowglobe on a shelf in the Unseen University, a wobbly shelf).
 * Such a device is invented in Noon Twenty Second Century, but it can only look into the past. The pictures it shows... aren't pretty.
 * In the science fiction novella E for Effort a man invents a time viewer which can see any past occurance. It doesn't have audio, they employ lipreaders to find out exactly what people are saying. Initially they use it to make films about the past.
 * The Fellowship of the Ring. The Mirror of Galadriel can show visions of the past and the future. Sam sees events that will occur in The Two Towers during his and Frodo's entry into Mordor, as well as events in the Shire after Saruman takes over. Frodo sees the fall of Numenor and the founding of Gondor, which occurred in the distant past.
 * Robert Heinlein short story "By His Bootstraps". The Time Gate can be used to look backward and forward in time as well as to travel to the time shown.
 * The Pensieve from the Harry Potter novels, which records and plays back memories, is a version of this.
 * Mirrors that work like this are mentioned in Septimus Heap.

Live-Action TV

 * The Doctor Who episode "The Chase" (with the first Doctor William Hartnell, and only the third Dalek story ever) features a Time-Space Visualiser which can view any event in history.
 * The Atavachron from Star Trek the Original Series.
 * In Star Trek Enterprise, the time traveller Daniels uses a device like this, while he is congratulating Captain Archer for successfully fixing the time stream.
 * The Twilight Zone episode "A Most Unusual Camera" has a camera that can see into the future.
 * The Time Tunnel. In addition to sending items and living beings through time, the scientists controlling the title device could also use it as a time viewer to see the past and the future.

Tabletop Games

 * GURPS Ultra-tech describes the "timescanner". It has very limited abilities: it can only display things in a two-yard radius, it needs days to focus on the specified moment in time, and it is only available in soft sci-fi settings anyway. And until a portable version is invented, the timescanner machinery occupies an entire room.

Theater

 * In The Golden Apple, Mother Hare gives Ulysses and Penelope a glimpse of a verdant valley turned into future wasteland, and presents them with a kaleidoscopic vision, projected in the form of woodcuts and lithographs, of the spectacular scientific achievements forthcoming in the twentieth century.

Web Comics

 * The clouds on Skaia in Homestuck are natural versions of this.
 * It's heavily implied that a device like this will show up in Girl Genius at some point... though so far we've only seen it from the "other side", as it were. At several points in the comic, strange "windows" suddenly appear hovering in mid-air, with doubles of some of the comic's characters standing on the other side, seemingly discussing what they're seeing as if they were watching events happening in their past.

Western Animation

 * My Life As a Teenage Robot
 * One of the villains in The Impossibles is shown using this to observe 20th-century events from the 40th century.
 * The various time-windows in Clockwork's lair in Danny Phantom.