This glass instrument— known as a tantalus cup or phythagorean cup, and used for parlor tricks and physics demonstrations—empties itself when the liquid reaches the height of the bend in the siphon. This example was used at Gettysburg College.
Ref: Benjamin Pike, Jr., Pike’s Illustrated Descriptive Catalogue of Optical, Mathematical, and Philosophical Instruments (New York, 1848), vol. 1, p.
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