NavList:

Brad, you wrote:
"Whew! In other words, estimate the alitude of the objects at the time that the distance was measured by using proportional logarithms! "

Bowditch here is recommending the very long way around. Very often, Bowditch's recommendations are efficient. Sometimes they are inefficient, like in this case. If I remember correctly, this is an example of advice that was in the first edition and never edited, never revised --at least not until late in the century. Using proportional logarithms and this highly detailed approach was quite un-necessary and there are other sources in the period that offer the simpler advice to shoot the altitudes and distances in the appropriate order and "average". They just leave it at that. You shoot the Moon's altitude, then the Sun's, then three or five lunar distances (noting only the time of the middle observation), then the Sun's altitude, then the Moon's altitude. You average the two Moon altitudes, average the two Sun altitudes, and average all the lunars. The observations are then equivalent to a single simultaneous set at the middle time. Since the altitude of the Moon matters least, you shoot it first and last. It's all very simple. Note that this method requires a fairly uniform sight-taking cadence with reasonably uniform intervals between the sights. I've done this many times, and it's not hard at all to do correctly. A good way to test your timing and convince yourself that you shoot at uniform intervals is to keep a voice recording so that you can check after the fact. I have been happily surprised at how nearly my sights would fall at two-minute intervals.

-FER

----------------------------------------------------------------
NavList message boards and member settings: www.fer3.com/NavList
Members may optionally receive posts by email.
To cancel email delivery, send a message to NoMail[at]fer3.com
----------------------------------------------------------------