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Stop press: siphon

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Red-faced lexicographers at the esteemed Oxford English Dictionary corporation have had their not very scientific knuckles rapped by — er — an Australian. Albeit an Australian who’s a physics lecturer.

Dr Stephen Hughes noticed that the word ‘siphon’ has an incorrect definition in the OED. It wrongly claims (and has done so for nearly a century) that ‘atmospheric pressure’ is involved. That, apparently, should be gravity.

Oxford Dictionaries also currently has the wrong definition, but interestingly, the compilers of my Oxford Dictionary of English (2006) can wear eau de smug today: their definition correctly describes the process of fluid being conveyed by gravity.

Read more on this in the Telegraph


12 Responses

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  1. ODE have it right. Atmospheric pressure drives the siphon, gravity is just along for the ride.


    11/05/2010 at 12:06 pm

  2. On reflection, it depends on the siphon. In a lavatory S-bend, it’s the weight of the water (gravity) that triggers the process. However, if you stick a hose in a tank, and suck, that’s atmospheric pressure.


    11/05/2010 at 12:09 pm

    • I bow to your superior knowledge, Ron!


      11/05/2010 at 12:23 pm

      • If it was just gravity, you could stick a hose in a tank, and liquid would flow. It doesn’t. But when you suck, creating negative pressure, atmospheric pressure, abhorring even a partial vacuum, pushes the liquid down the hose to fill up the void, causing it to flow.

        As that annoying meerkat says, Simples!


        11/05/2010 at 12:33 pm

        • So the Aussie expert is wrong and the OED shouldn’t be correcting its entry?


          11/05/2010 at 12:37 pm

          • Both are correct – for a given value of correct. It depends on the type of siphon – simple, or S-trap, to give it it’s proper name.

            Maybe it all works differently upside-down?


            11/05/2010 at 12:40 pm

            • That’ll be it — the upside-down thing. The OED bods haven’t twigged yet.


              11/05/2010 at 12:43 pm

  3. As I said before, though, gravity is along for the ride – atmospheric pressure, when you suck the hose, starts the process, gravity ensures the liquid “falls” out of the end of the hose. That’s my view, anyway.


    11/05/2010 at 12:43 pm

  4. Just had a look at the Telegraph:-

    “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,” Dr Hughes said.

    So I wasn’t wrong (when I said it was rubbish), but he completely ignores the fact that atmospheric pressure starts the process by getting water into the longer arm, even if gravity finishes it.

    Bet you’re sorry you started this…


    11/05/2010 at 2:36 pm

    • It’s a really strange one, isn’t it? I wonder how accurate the actual coverage of the story is. You are right to question it — I fell for it and took it at face value. It’s a bit like an egg-heady April Fool’s Day newspaper spoof.


      11/05/2010 at 3:08 pm

      • It’s like sucking a drink up a straw – atmospheric pressure does that – as before, the suck creates a partial vacuum, and atmospheric pressure (which is a powerful force and can’t just be ignored, as the Oz guy seems to be doing), pushes the drink up the straw. Just like starting a siphon.

        But you’re right – something odd going on there.


        11/05/2010 at 3:27 pm

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