Oops--Siphon Definition Defied Law of Gravity

Oops--Siphon Definition Defied Law of Gravity

This week Australian physicist Dr. Stephen Hughes of the Queensland University of Technology found an error in the Oxford English Dictionary (OED), and he is having it corrected. The definition in question is for the word “siphon.” The definition, which has been followed by most other dictionaries, has been in error for the last 99 years. The following is the OED definition:

A pipe or tube of glass, metal or other material, bent so that one leg is longer than the other, and used for drawing off liquids by means of atmospheric pressure, which forces the liquid up the shorter leg and over the bend in the pipe.

Margot Charlton of the OED’s staff explained, “The OED entry for siphon dates from 1911 and was written by editors who were not scientists.” She was surprised that nobody had queried the definition in those 99 years. The definition of siphon will be corrected in the next edition of the OED.

Atmospheric pressure is involved to start the process of moving the liquid up the shorter leg of the siphon. However, once the fluid is over the bend in the tube, it is gravity, the weight of the liquid, that pulls the it down the longer leg.

Dr. Hughes reported, “An extensive check of online and offline dictionaries did not reveal a single dictionary that correctly referred to gravity being the operative force in a siphon.” I guess he did not check Merriam-Webster’s 11th Collegiate Dictionary, which provides the following definition:

1 a : a tube bent to form two legs of unequal length by which a liquid can be transferred to a lower level over an intermediate elevation by the pressure of the atmosphere in forcing the liquid up the shorter branch of the tube immersed in it while the excess of weight of the liquid in the longer branch when once filled causes a continuous flow

Amsco has editors who are scientists, but we are human and sometimes make a mistake. Like the OED, once we become aware of it, we correct it in the next reprint.

I got the idea for this post from my son, Don, who sent me a link to an article in The Register, an Information Technology journal from the United Kingdom. I enjoyed the article so much that I subscribed. On Tuesday, I saw the following headline in the science section of The Register: “Siphon Wars: Pressurist Weighs into Gravitite Boffin. This could be trouble, I thought, and it was. Rather than try to paraphrase (see tomorrow’s post by Lauren), I decided to quote from The Register.

Hello from Colorado, USA -

     Your article describing the grumblings of a physics professor who claims that atmospheric pressure is not the operative force in a siphon (posted in Physics, 10th May 2010) lacks one essential detail--the "professor" is wrong. Gravity is indeed involved in a siphon's activity: It draws water downward in the outflow leg, lowering the pressure inside the leg. However, without pressure at the mouth of the inflow leg to drive the liquid upward, siphoning will not occur. Without atmospheric pressure, siphons (and drinking straws, by the way) won't work, even where there's gravity.

     Air "weighs" about 14.7 pounds per square inch of area on which it rests, including the surface of a liquid; this pressurizes the liquid to this amount. When you "suck" on a straw, you are reducing the pressure at the mouth end of the straw, and the pressure at the other end drives the liquid into your mouth. The downward side of a siphon "sucks" the same way.

     Maybe the academic in question is into first causes: It is true that atmospheric pressure is the result of gravity "pulling" air downward and compressing it, but saying that atmospheric pressure isn't relevant to siphoning is idiotic...

     Put more simply, try sucking on a straw or siphoning in a vacuum--it won't work. Ask a physicist.

     Yours truly, Robert Weaver Colorado Springs, Colorado, USA

     P.S. Siphons more than 32 feet high don't work at all--not enough atmospheric pressure. P.P.S. Perform a service to English-speakers everywhere! Inform the OED folks that they might want to think twice before revising their definition of a siphon.

Now I’m confused. Maybe I should cancel my subscription to The Register.