Next message: Frank Reed: "Re: Almanac Heaven"
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
