Dictionary definition of 'siphon' has been wrong for nearly a century

[WillParkinson]

Dictionary definition of 'siphon' has been wrong for nearly a century

A schoolboy error in the Oxford English Dictionary's definition of 'siphon' has come to light after nearly 100 years in print.


Perpetuated by dictionaries for nearly a century, it's surely the most persistent scientific howler in the history of the English language. Siphons – those ingenious plastic tubes we use to fill or drain everything from aquariums to petrol tanks – move liquid by "the force of atmospheric pressure".

Except, how could a siphon possibly work by a difference in pressure when atmospheric pressure is the same for the liquid at both ends of the tube? Bleeding obvious when you think about it. Even I can figure that out 25 years after I scraped through A level physics.

http://www.guardian.co.uk/science/blog/2010/may/10/dictionary-definition-siphon-wrong

[rug]

1. That sucks.

[WillParkinson]

2. Congrats!

I was wondering who'd be the first to say it. :-)

[struggle4progress]

3. Guardian, bitching about OED explanation, itself gives wrong explanation

Guardian says: "Once the liquid has passed the highest point in the tube, the continuous chain of cohesive bonds between the liquid molecules in the tube, and the force of gravity, do the rest"

Whenever the "continuous chain of cohesive bonds between the liquid molecules in the tube" plays a major role, one should be able to siphon liquid, even if the exterior end of the tube is above the level of the liquid in the reservoir, provided that the liquid falls from the exterior end of the tube to a level below the level of the liquid in the reservoir. But this is not what one generally sees: the siphon fails as soon as its exterior tube end is at or above the level of the liquid in the reservoir

The proper correction of the OED entry is simply to strike the word "atmospheric" from the definition: the siphon works as long as there is a pressure difference between the two ends of the tube, with the exterior end being at lower pressure than the interior end. The weight of the fluid in the reservoir, above the interior end of the tube, produces the extra pressure on the interior end of the tube, accounting for the pressure difference

[Orrex]

4. This thread makes me have to go pee.