Supposedly, an early Millikan oil drop experiment apparatus (in a basement at Caltech)

Millikan's oil-drop experiments are justly regarded as a major contribution to twentieth-century physics. They established the quantization of electric charge, the existence of a fundamental unit of charge, and also measured that unit of charge precisely.

Source

A while ago, I interned a summer at a Caltech thing. I was studying physics at the time and met another physics undergrad there, who showed me some of the cooler bits of the school.