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    Re: Sextant Accuracy and anomalous dip
    From: Nels Tomlinson
    Date: 2003 Mar 21, 20:39 -0900

    We read in the story that the ``electricians'' could make measurements
    to determine how far down the cable the fault lay.  That tells us that
    they did know the propagation speed for the cable.
    
    The way this works is that you send a signal down the cable, and measure
    the time it takes for the reflection to return from the short.  If you
    know the propagation speed, you know the distance, and otherwise, you
    don't.  I've done this with an oscilloscope and signal generator.  You
    can also buy an instrument which combines the two, called a time-domain
    reflectometer.
    
    I'm not sure how they did it back then.  It may be that they measured
    the resonant frequency of the shorted cable (or a circuit consisting of
    the shorted cable and a known capacitor), and calculated the length of
    cable which would produce that frequency.
    
    I've just realized that my knowledge of EE history is quite weak.
    
    Nels
    
    
    
    Rodney Myrvaagnes wrote:
    > On Fri, 21 Mar 2003 18:53:37 EST, Bruce Stark wrote:
    >
    >
    >>I expect he already had the longitude. It's only reasonable to suppose that,
    >>as soon as a cable was laid, Greenwich time was telegraphed from an
    >>observatory so observers at the new station could determine the station's
    >>exact position. By finding the local time at the station, and applying the
    >
    >
    > Reasonable if they had previously measured the propagation speed for
    > the cable.
    >
    > Any records of them doing this?
    >
    >
    >
    >
    > Rodney Myrvaagnes                                                    J36 Gjo/a
    >
    >
    > "We have achieved the inversion of the single note." __ Peter Ustinov as Karlheinz Stockhausen
    >
    
    
    

       
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