A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Ducruy Jacques
Date: 2015 Aug 3, 01:06 -0700
Thank you very much for the paper of Mendoza Rios : very good summary of the problem of double altitude !
The method of Douwes is interesting, because it is very "mathematical" => the calculation of mean hour angle is a "system of 2 equations" : this is not the case of the another methods (Duillier or Dunn).
Another point of interest : the formula giving the latitude had been use also for the ex-meridian problem (see Norie, edition 1814 for example) : I suppose that Douwes is the "creator" of the two methods : first latitude by double altitude (1740), and second the method of ex-meridian (17??).
I have speak of the method of Borda, witch had some commun points with Douwes : calculation of HHA first, then calculation of latitude, by a rigourous formula (righht angled triangle) : but it seems that the method of Borda is unknow in UK or USA. Thhe method of Borda had been simplified by Ducom (1806).