A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Lars Bergman
Date: 2019 Jan 3, 11:37 -0800
Frank, you asked (in A lunar in 1845)
"Does anyone know (or can anyone suggest) an alternate meaning for "lon in"?"
The expressions latitude in, and longitude in, were common in connection with traverse table work, or logarithmic traverse calculations. There you always deal with two different positions, the "from" position and the "arrived at" position. These were called latitude/longitude left, and latitude/longitude in, respectively. In my Bowditch from 1851, several examples can be seen in the chapter of Plane Sailing, also in the chapter Methods of Keeping a Journal at Sea. So one guess is that you saw "lon in" in connection with a dead reckoning position, or else it could have been an ordinary a.m. sight for longitude that was brought forward to noon by a traverse table look-up.
Lars 59°N 18°E