Siphon
2 of the 6 encyclopedias on this shelf carry an entry for Siphon. Both are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
si'fon, a device for carrying liquids over an obstacle from one level to a lower level. The siphon in common use has the form of a bent tube with arms of unequal length. The shorter is the receiving arm. The intervening height over which a liquid may be siphoned is the height to which atmospheric pressure would raise the liquid. It corresponds to the barometric column, and is for water the same as the height to which water may be raised by the ordinary lift pump at sea level. Water may be siphoned over an obstacle thirty feet high. The air must be exhausted from the siphon in order that the water may rise as a consequence of atmospheric pressure. This may be done by means of suction by the mouth or by a pump; or the siphon may be filled with the liquid which is to be removed, and placed in position while still filled. In either case, the water in the long arm tends to run out and create a vacuum at the top of the bend. Atmospheric pressure on the supply surface forces water up the short arm to keep the pipe full. There is no limit as to size. An air-tight city aqueduct works on the same principle as a slender tube.
Collier's New Encyclopedia (1921)
a curved tube having one branch longer than the other; used for transferring liquids from higher to lower levels. It acts by atmospheric pressure, and consequently cannot be depended on for overcoming heights greater than about 30 feet near the level of the sea, and a less height at greater elevations.
What Has Changed in the Last Century
The practical account is still correct: a water siphon near sea level will not lift over roughly 30 feet, and every flush toilet and aquarium hose still works as Aiton's described in 1910. What has moved is the explanation. Both entries credit atmospheric pressure alone, but experiments published since 2010 — including one in which a siphon ran inside a vacuum chamber using a degassed ionic liquid — showed that the cohesion, or tensile strength, of the liquid column also carries the flow, and that a chain-like pull between molecules can sustain a siphon where air pressure cannot. The point was public enough that in 2010 the Oxford English Dictionary was reported to have amended its own definition, which had attributed siphon action solely to atmospheric pressure.
Written for this edition, 2026.