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I'm guessing that a "Heath-Robinson arrangement" is the English
equivalent of the American "Rube Goldberg device,"

gl

George Huxtable wrote:
> Wayne, via "Rebecca Lowry" , asked-
> about "Longitude by meridian transit/ fishline sextant"
>
>
> Cool,
> A new toy to make....
>
> Any idea what the numbers on page 2-109 for the year are?
> And how do we find the numbers for the current year?
> Wayne
>
> ===========
>
> Those numbers sum up to provide GHA Aries, in arc-minutes. But for this
> application, it's absurd to bother allowing for such a year-to-year
> variation. If a constant value of around 35 was chosen, unchanging from year
> to year, that would be perfectly compatible with the precision that the
> method is capable of providing.
>
> The claim is, as Mike Boersma repeats, a precision in precision of 10 miles,
> which requires latitude and longitude to be within one sixth of a
> degree.That would require the following quantities components to be known,
> or set, within the appropriate accuracies, all within 10 arc-minutes.
>
> GMT to 40 seconds (quite plausible)
> A pendulum string, some few metres long, hanging steady and vertical in the
> open air, with no shielding from wind.
> Another string, a few metres long, set accurately horizontal, with no
> guidance given as to how to achieve that.
> That horizontal string to be set precisely in a North-South direction "by
> using a compass". No mention of variation.
> Another diagonal string, tensioned to be straight enough to measure an angle
> from, attached part-way up the length of the vertical pendulum, which
> doesn't kink that vertical string out of straight.
> A paper protractor, for measuring the angle between two bits of string in
> space.
>
> All these are supposed to combine together to give a precision in the result
> amounting to 10 arc minutes!. With such a Heath-Robinson arrangement, anyone
> who got the answer right within a couple of degrees, or 120 miles, would be
> doing well.
>
> There's nothing wrong, in principle, with any component of this scheme. But
> it's a procedure that looks as if it's been assembled by a committee, given
> the job of knocking up some sort of emergency manual. Completely
> unrealistic.
>
> George.
>
> contact George Huxtable, at  george@hux.me.uk
> or at +44 1865 820222 (from UK, 01865 820222)
> or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
>
> =====================
>
>
> --- On Mon, 2/15/10, Mike Boersma  wrote:
>
>
> From: Mike Boersma 
> Subject: [NavList] Longitude by meridian transit/ fishline sextant
> To: NavList@fer3.com
> Date: Monday, February 15, 2010, 12:48 PM
>
>
>
> The US Airforce survival manual from the 1960's included a description of
> how to make a fishline sextant and tables for determining longitude and
> latitude from its use.
> The claimed accuracy is 10 miles. Individual results may vary.
> Mike Boersma
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