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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Artificial horizon
From: Bruce Stark
Date: 2005 Feb 20, 17:13 EST
From: Bruce Stark
Date: 2005 Feb 20, 17:13 EST
Robert,
I've been following the artificial horizon thread with considerable interest. Thank you for the address of the Smithsonian article.
For sun observations, the advice Major Ellicott gave Lewis is the best I know of. Several years ago I was taking observations at Great Falls, and got an excellent noon latitude when the wind was blowing some thirty knots. Gusts shook me, but the water stayed calm. The pan was on the ground, of course, otherwise it would have picked up vibrations from what it was on.
Regarding that "block of talc," I don't think it was for a reflecting surface. Professor Bergantio, the authority on Lewis and Clark's camping spots, told me that mineralogists informed him "talc" meant "isinglass." This solved a puzzle for me. Lewis and Clark used a quadrant for most of their artificial horizon work, and quadrants didn't normally have horizon shades. I'd wondered how they protected their eyes from the glare of the sun's reflection in the water. It also solved a puzzled for Bergantino. He'd wondered what the isinglass was for. Together we conjectured that the block of isinglass was split into sheets to use as the transparent part of the cloche protecting the water pan. It would have been dark, and far less likely to be broken than glass.
In case anyone wants to make the wooden ball and mirror horizon mentioned in the Bedini article, they should know it was half a ball, with the glass cemented to the flat side. The round part sat in a triangular hole in a platform, so the glass could be roughly leveled by shifting the ball. I believe the final adjustment was made to the platform itself, with screws.
Bruce
I've been following the artificial horizon thread with considerable interest. Thank you for the address of the Smithsonian article.
For sun observations, the advice Major Ellicott gave Lewis is the best I know of. Several years ago I was taking observations at Great Falls, and got an excellent noon latitude when the wind was blowing some thirty knots. Gusts shook me, but the water stayed calm. The pan was on the ground, of course, otherwise it would have picked up vibrations from what it was on.
Regarding that "block of talc," I don't think it was for a reflecting surface. Professor Bergantio, the authority on Lewis and Clark's camping spots, told me that mineralogists informed him "talc" meant "isinglass." This solved a puzzle for me. Lewis and Clark used a quadrant for most of their artificial horizon work, and quadrants didn't normally have horizon shades. I'd wondered how they protected their eyes from the glare of the sun's reflection in the water. It also solved a puzzled for Bergantino. He'd wondered what the isinglass was for. Together we conjectured that the block of isinglass was split into sheets to use as the transparent part of the cloche protecting the water pan. It would have been dark, and far less likely to be broken than glass.
In case anyone wants to make the wooden ball and mirror horizon mentioned in the Bedini article, they should know it was half a ball, with the glass cemented to the flat side. The round part sat in a triangular hole in a platform, so the glass could be roughly leveled by shifting the ball. I believe the final adjustment was made to the platform itself, with screws.
Bruce
