Professor Hughe' definition can be found here and he claims that the siphon action has been demonstrated in a vacuum (footnote 3.)
His explaination relies solely on gravity and the molecular attraction of individual water molecules to form a "chain" that is pulled up and over the hump, in the same way that a chain and pulley work.
It would be simple to test which theory (atmospheric pressure or gravity alone) is correct by building two sealed boxes connected by a flexible hose. Each box would be halfway filled with liquid, then the atmospheric pressure drawn out of the empty space above the liquid in both containers. Once the hose is filled with water, lowering one container below the other container should begin liquid transfer. Switching the positions of the two boxes should reverse flow. If water flows, then gravity is the root cause of the siphon action.
Alternately, one Atmosphere is roughly equal to 34 feet of water. Try to create a siphon that can lift water higher than 34 feet before it makes it's turn downwards. If the siphon action stops when the lifted column of water exceeds 34 feet, then atmospheric pressure is the root cause of the siphon action.
Professor Hughe' definition can be found here and he claims that the siphon action has been demonstrated in a vacuum (footnote 3 2.)
The scientific method doesn't work by hypothesis and experimental proof. It proceeds by consensus and by considerations of social justice. Oh, and the assertions of C-list celebrities.
The debate is over. Siphons used to work by air pressure 99 years ago, but man's destruction of air pressure's native habitat has changed the way they work, for ever.
P.S. I have Siphon Credits to sell.
To take water up a tube that does not have an effective prime requires drafting. Drafting is driven by atmospheric pressure. The maximum theoretical lift at sea level is roughly 33.8 feet. A column of water 1 foot tall exerts .434 psi at the base. 14.7/.434 gives us the 33.8. Siphoning, OTOH, is not dependent upon atmospheric pressure, but on the vacuum created in the hose when water drains out the other end.
If you had to draft to lift your water to start the siphoning process, there would be a maximum theoretical lift. I do not know what the results would be if a 100 foot hose were plugged and lifted over a 35 foot wall then back to below the level of the water in the original container, but I suspect it would still siphon.
I stand corrected. I hadn’t considered the molecular attraction between the water molecules. That’s what I get for posting before thinking.