Causes a living being to rapidly cycle through youth and old age.
The bell jar is large and made of crystal. It was producing a dancing, diamond-bright light. Drifting along in the sparkling current inside was a tiny, jewel-bright egg. As the egg rose in the jar, it cracked open and a hummingbird emerged, which was carried to the very top of the jar, but as it fell on the draught its feathers became bedraggled and damp again, and by the time it had been borne back to the bottom of the jar it had been enclosed once more in its egg and then repeating this process over and over again.
In 1996, during the Battle of the Department of Mysteries, Harry, Hermione, Ron, Ginny, Luna, and Neville saw a towering crystal bell jar that stood inside the Time Room in the Department of Mysteries as they made their way into the Hall of Prophecy. Later on, in the battle, one of the Death Eaters who attacked them accidentally stuck his head through the bell jar after Hermione used the Stunning Spell on him. The Death Eater's head was transforming into the head of a baby; as he struggled to get up again, his head returned to its previous proportions, but before he could pull himself together, his head once again began to shrink back to babyhood.