A fluid link was a component of a TARDIS essential for providing power to the ship, resembling a small glass rod. Fluid links required mercury to function. The First Doctor falsely claimed that the TARDIS' fluid link had run out of mercury as a ruse to explore the Dalek City. The link was later confiscated by the Daleks and accidentally left behind in the city, forcing the time travellers to help the Thals fight the Daleks to recover it. (TV: The Daleks) While the TARDIS was being brought to the Animus by the Zarbi, Vicki accidentally re-aligned the fluid link, which restored power to the ship. (TV: The Web Planet)