An eagle-eyed Australian scientist has forced the Oxford English Dictionary to change its definition of how a siphon works, after he found an error in the entry which had gone unnoticed for 99 years.
For almost a century, the dictionary incorrectly stated that atmospheric pressure, rather than gravity, is the operating force in a siphon, researchers said.
In 2010, Dr Stephen Hughes from the Queensland University of Technology spotted the mistake, which went unnoticed for 99 years.
For Exploring the boundary between the siphon and barometer in a hypobaric chamber, Hughes conducted an experiment in a hypobaric chamber, which simulates the effects of high altitude.
A siphon 1.5 metres high was set up in the chamber and when the pressure was reduced to an altitude of 40,000 feet a waterfall appeared at the top, but the water flow remained nearly constant.
At 41,000 feet, the siphon broke into two columns of water and, when returned to 40,000 feet, it reconnected as if nothing had happened, researchers said.
Atmospheric pressure at 40,000 feet, which is more than 10,000 feet higher than Mount Everest, is about 18 per cent of the sea level value, they said.
For the experiment, two buckets, one higher than the other and connected by tubing, were set up and a pool pump returned water from the lower bucket to the higher bucket.
"The fact that the water level in the upper and lower buckets is constant indicates that atmospheric pressure is not pushing water into the siphon," Hughes said.
"The stable water surfaces act like energy barriers between the atmosphere and siphon. For energy to be transferred from the atmosphere to the water the water level would have to go down, since the amount of energy transferred is equal to force times distance," said Hughes.
"If the water level is constant the distance is zero and therefore no energy can be transferred," he said.
Hughes said siphon, a tube used to convey liquid upwards from a reservoir and then down to a lower level of its own accord, had been used since ancient times but how it works was still debated.
"If you think of a car, atmospheric pressure is like the wheels, it enables it to work. But gravity is the engine," he said.
"It is gravity that moves the fluid in a siphon, with the water in the longer downward arm pulling the water up the shorter arm," said Hughes.
According to Hughes, the Oxford English Dictionary corrected the error and removed the reference to atmospheric pressure after he pointed it out.
However, he said the new entry "unfortunately remains ambiguous".
The finding was published in the journal Scientific Reports.