To moderator - I had mistakenly posted this to the "General Physics" forum and later noticed the note about not posting there - sorry! I hope this is the correct location for posting the following question. I am a novice on this site and am trying to find an answer to a question which is: I filled a tube 48" x 1.5" with water, sealing one end and then inverted it - I expected the water to remain due to the vacuum but it did not. Is there a certain ratio of ht. to dia. required to keep the water in the tube? I would appreciate any imput, guidance or direction on this....Thank you!