- "The source of the light, the crystal bell jar quite as tall as he was that stood on a desk and appeared to be full of a billowing, glittering wind."
- —Description of the Bell jar[src]
A bell jar is a piece of laboratory equipment similar in shape to a bell. It is located in the Time Room, a room in the Department of Mysteries that studies time on Level 9 of the Ministry of Magic.
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 small 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.
- "It was shrinking very fast, growing balder and balder, the black hair and stubble retracting into his skull, his cheeks smooth, his skull round and covered with a peachlike fuzz. . . . A baby’s head now sat grotesquely on top of the thick, muscled neck of the Death Eater as he struggled to get up again. But even as they watched, their mouths open, the head began to swell to its previous proportions again, thick black hair was sprouting from the pate and chin. . . ."
- —A Death Eater under the effects of the Bell jar[src]
Further in the battle, a Death Eater (possibly Rabastan Lestrange or Crabbe Snr.) 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 transformed 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.
- Harry Potter and the Order of the Phoenix (First appearance)