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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: H.O. 203/204, Littlehales, Hydrographic Engineer
From: Brad Morris
Date: 2017 Mar 22, 10:41 -0400
From: Brad Morris
Date: 2017 Mar 22, 10:41 -0400
Bob
Yes, there is specific interpolation assistance!
For each dependent value of Hour Angle, there is an increment provided for each 1' of change in declination. Similarly for azimuth.
The dependent Hour Angle is a function of the true altitude, given generally in 1° steps. The interpolation assistance is for each 1' change in declination. That is, the dependent hour angle changes as the independent variable (declination) changes. So as we look up, using a whole number for Latitude, a whole number for Declination and a whole number for true altitude, we obtain dependent values Hour Angle and Azimuth. Those values are changed by each 1' of additional Declination from the whole value used in the lookup.
I certainly surrender on the point of primacy. I wonder why Littlehales did not reference that prior text? One wild guess: it took time to create tens of thousands of entries for 1600 pages and check them. Perhaps HO 201 didn't exist when Littlehales conceived of the table, but 201 beat him to print??? That is a total guess, and again, I cannot support it.
Brad
On Mar 22, 2017 10:25 AM, "Robert VanderPol II" <NoReply_RobertVanderPolII@fer3.com> wrote:
Brad:
It sounds like this may have been the 2nd inspection table as opposed to mathematical tables like Weems, Driesenstock or Ageton.
My 1984 edition of Bowditch lists HO-201 (1919,Simultaneous Altitudes and Azimuths of Celestial Bodies) which it describes as a lookup table. 606pg, Lat to 60o, Dec to 24o, LHA tablulated every 2.5o. It comments that the tables were well arrange but no assitance was given for interpolation of declination. Based date and HO number this appears to pre-date 203/204. Does 203/204 give interpolation assistance? The expanded range explains the table growth.
Thanks for the info.
Bob II
