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    Re: H.O. 203/204, Littlehales, Hydrographic Engineer
    From: Robert Pearson
    Date: 2017 Mar 23, 16:09 -0700

    I've been following this topic with some interest.

    I suggest anyone interested check a copy of HO Pub 9 aka Bowditch, 1962 version which contains a chapter on various sight reduction methods. IIRC 1958 was the 1st version to include this - but it's not found in the lastest version of Pub 9. The chapter is a faily complete review of most of the methods of sight reduction used and proposed over the previous 190 years. I have to think that this has been mentioned before in the navlist archives.

    "Comparision of Various Methods of Sight Reduction", Chapter XXI in my 1962 version, list several inspection tabular methods for solution of meridian angle and also altitude and azimuths. It states the first "inspection tables"  were probably prepared by M. Cassini in 1770. So the solution by inspection table lookup and interpolation for meridian angle has been around a long time. For altitude and azimuth it's much shorter but probably since 1907.

    I found 11 authors listed who provided inspection tables prior to the advent of the modern tables which started with HO 214 (1936-1946). I note that Janet Taylor, despite her many accomplishments, was not listed.  

    Authors listed for solution of meridian angle are:
    M. Cassini (1770)
    LaLande (1793)
    Lynn (1827)
    Hommey (1863)
    Davis (1897)
    Blackburne (1914)
    Littlehales (1923, HO 203 & 204)

    It states that Littlehales' arrangement is similar to that of both Davis and Blackburne.

    Some of the above include a solution for azimuth which allows plotting of LOPs or Sumner Lines without 2 solutions for meridian angles if so desired. I think any could be used to solve a timesight for longitude.

    Authors listed for solutions of altitudes and azimuths are:
    Ball (1907)
    Davis (1917)
    HO 201 (1919 uncredited)

    Regards,
    Robert Pearson

       
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