Jan Tregeagle was reputed to be an evil lawyer who sold his soul to the Devil, as a result of which his ghost was given endless tasks by clergymen in an attempt to save it. one of these tasks was to empty Dozmary Pool (said to be bottomless) with a leaky limpet shell.
This atmospheric pool is also one of many places where Sir Bedivere is reputed to have throw away the sword Excalibur at King Arthur’s command as he lay dying, with a hand emerging from the water to grasp the weapon.