NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
"Sumner" before Sumner
From: Frank Reed CT
Date: 2006 Mar 30, 19:06 EST
From: Frank Reed CT
Date: 2006 Mar 30, 19:06 EST
Some history fun. In 1826, an appendix by W. Lax was published in the Nautical Almanac for the year 1829. It's a method for using altitudes of two different objects taken simultaneously (more or less) to get a complete fix of a ship's position. It yields latitude and local apparent time (and hence longitude if we can get GMT) with one calculation based on those measured altitudes. It's long and not particularly practical. The emphasis is on observations taken for a lunar distance observation which complicates the analysis. If Lax had instead focused on altitude observations with Greenwich Time "given" by some abstract method, the whole process might have appeared much more relevant to practical navigation, and he might have "scooped" Sumner who published his graphical method almost 20 years later. Lax got close, but he didn't see the big picture. Lax even talks about error analysis (which I mentioned in an earlier message) and notes that this method of fixing the position is prone to error when the relative azimuth between the two bodies is low and is least prone to error when the relative azimuth is close to 90 degrees --which of course is very familiar to 20th century navigators as the result of the crossing angle between two celestial lines of position. -FER 42.0N 87.7W, or 41.4N 72.1W. www.HistoricalAtlas.com/lunars
