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Suppose the column of fluid, when streched into a straight-tube, measures x. Given any cross-section of the fluid in the tube, the pressure on it measures 0. Let's look at this in detail:

Consider a cross-section of fluid at some distance h below the surface of the fluid. The pressure on one side of the fluid is

[tex]P_0 + \rho h g[/tex]

where [itex]P_0[/itex] is the atmospheric pressure and [itex]\rho[/itex] is the density of the fluid. The pressure on the other side is

[tex]P_0 + \rho (x - h) g[/tex]

Since the pressure on both sides are equal, equating the two equations above yields h = x - h. This, of course, is only possible if the cross-section is in the middle of the tube (h = x/2). Hmm...did I miss something here?