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On Thu, Feb 12, 2015 at 4:46 PM, David Pike  wrote:
>...how William Bligh might have done a compass check...

The pilots now their azimuth attend,
On which all courses, duly form'd, depend :
The compass placed to catch the rising ray,
The quadrant's shadows studious they survey;
Along the arch the gradual index slides,
While Phoebus down the vertic-circle glides;
Now seen on ocean's utmost verge to swim,
He sweeps it vibrant with his nether limb.
Thus height and polar distance are obtain'd,
Then latitude, and declination, gain'd ;
In chiliads next the analogy is sought,
And on the sinical triangle wrought:
By this magnetic variance is explored,
Just angles known, and polar truth restored.

- William Falconer, The Shipwreck

Don Seltzer

   

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