NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Marty Lyons
Date: 2023 Jun 25, 11:30 -0700
The Abney level works basically like a sextant with a bubble horizon attachment. The Abney has a scope with crosshairs and a split viewing screen. On one side of the view is the object at a distance, then the level bubble is seen on the left half of the view. It's just like a split horizon mirror except instead of seeing the horizon you see the bubble which gets lined up with the crosshairs. There is a protractor arrangement which allows the level to swivel as the scope is inclined for viewing objects above the horizon. In the surveying field, its called a hand level, used for doing earthwork grading projcts. I have adapted an IR850 camera filter to the scope to allow safe sun viewing. The entire unit is much lighter thean a sextant which makes holding it steady difficult. This level could never be used on a rocking boat. I have clamped it to a ball head on a tripod for steadiness, just to see if the procedure is even doable for fixes. Similar to not having to worry about dip with a bubble horizon sextant or aircraft sextant, I would not use dip in any calcualtions. I do think , however, that if using a natural horizon to establish the index error of the instrument, I would have to figure dip in. An Abney level is simply the adjustable version of a hand level for measuring slopes. It's essentially the same as the Celestaire bubble attachment but with spirit level mounted to a protractor. The spirit level bubble is projected into the split screen scope view by a mirror arrangement.
