At 11:30 p.m. Wednesday, after the streets were clear of trick-
or-treaters and parties were winding down, a group of Caltech
students were pushing crates of frozen pumpkins up the elevator
in Millikan Library. There were about 50 pumpkins of various
shapes and sizes in all. As part of a Halloween tradition dating
back to 1972, five students climbed a ladder to the tallest
point of the roof and prepared to launch the pumpkins, frozen in
liquid nitrogen, off the side of the nine-story building. “I
don’t know anywhere else where you can see a pumpkin drop from a
building,” said Kelly Douglas, a development research specialist
at the campus. Hosted by Caltech’s Dabney House, the tradition
began as an experiment to test the theory that dropping a frozen
pumpkin from a significant height would produce blue-green
sparks, an event called triboluminescence, when it shattered.
The pumpkin-drop experiment is a play on the oil-drop experiment
conducted in 1909 to measure an electron’s charge by Caltech co-
founder Robert