The Humber Bridge

Q. If the earth is flat, why do top of the pylons of the Humber Bridge deviate in distance horizonally by 36mm?

A. The pylons were built vertically in relation to the earth. The pylons were built to be exactly the same height. The difference in horizontal distance at the top of the pylons is only a theoretical figure for what the difference should be if the earth were a globe.

No physical measurement of distance deviation was ever detected on this or any other bridge. Forum user "Niceguybut" once tried to champion the cause that there was a physical, detected difference on the Humber Bridge. Here were his results:

Niceguybut wrote:

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"I once tried to champion this cause, and in the interests of getting a definitive answer, I emailed the Humber Bridge Authority to ask whether the figure was measured or purely theoretical. Here's the reply:

    Thank you for your recent email.
    
    The two towers are build vertical to a tangent to the earth, i.e. radial to the 
    centre of the earth, thus, theoretically, the shape between the two towers is an 
    inverted trapesium rather than a rectangle with the length between the bottom of 
    the towers being 36mm less than the length at the top of the towers.
    
    The gap at the base is, of course, the one that was actually "measured" with the 
    apparent increase being a result of building the towers "vertically".
    
    Regards
    
    Peter Hill
    General Manager & Bridgemaster

So there you have it, straight from the horse's bridgemaster's mouth. I'm man enough to admit I backed a wrong 'un, so can we let this one go now?"

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