Originally Posted By: rafowell
Originally Posted By: Russ
Gravity doesn't work well enough in a small boat bouncing around at sea. I was a tad confused by the picture of the improvised sextant.
Measuring the angle between sun/star/planet and the horizon is much more consistent than using gravity. A sextant allows for ship movement while allowing an accurate elevation angle.

I don't think any measure of gravity (local vertical) was required.

The way that type of signal mirror sight works[1] is that you align the reflected light beam from the sun with the line between the hole in the mirror and the hole in the sight.

My guess is that he did that, with the horizon as the target, then recorded the mirror tilt angle, and doubled it to get the sun to horizon angle.



I came to the same conclusion. Somebody else would have to read the protractor while he was aiming it. There would have to be some extra mathematics to compensate for the vertical travel of the center of the mirror's sighting hole, but not impossible with a working knowledge of trigonometry (and mathematics tables).

As far as gravity goes, you are right that gravity dependent instruments don't fare too well in rough seas. However, gravity dependent sextants were used in aircraft until the 1960's demonstrating that they could be "good enough".
_________________________
Hope for the best and prepare for the worst.

The object in life is not to be on the side of the majority, but to escape finding oneself in the ranks of the insane