Definition of "pycnometer"

As Galileo showed in his tract La Bilancetta, or “The Little Balance,” a scientist of Archimedes’ stature could have achieved a far more precise result using his own law of buoyancy and an accurate scale, something far more common in the ancient world than a very precise pycnometer, which is used to measure displacement.

2006 December 8, David Biello, “Fact or Fiction?: Archimedes Coined the Term ‘Eureka!’ in the Bath”, in Scientific American