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    Re: Biruni and the radius of the Earth by dip
    From: Gary LaPook
    Date: 2011 Jan 7, 09:51 -0800
    I saw a device just like this for sale at a hardware store. It consisted of two clear plastic pipes about two feet long, one had a male fitting and the other had a female fitting so they could be attached to a common garden hose.


    --- On Thu, 1/6/11, George Huxtable <george@hux.me.uk> wrote:

    From: George Huxtable <george@hux.me.uk>
    Subject: [NavList] Re: Biruni and the radius of the Earth by dip
    To: NavList@fer3.com
    Date: Thursday, January 6, 2011, 4:32 PM

    "As you suggested in your first post on this, a water level will provide an
    excellent true horizontal level."

    Is Frank (and John Huth too) suggesting that a flexible pipe and a pair of
    vertical glass tubes be used, then, to provide a suitable level, to measure
    to an arc-minute? (Not, of course, that such technology was available to
    al-Biruni.). I wonder whether either of them has ever tried to make, and
    fill, and use, such a levelling device? The problem is to avoid entraining
    air-bubbles, which will then collect at any humps in the tube, unbalance
    the water-columns, and result in a false reading. If it was so simple in
    practice, buiders would use such devices in place of spirit-levels and
    theodolites. Just try it out, with a few metres of transparent plastic
    tube. Hint: use distilled, or at least boiled water, to reduce dissolved

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