A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David Pike
Date: 2016 Aug 26, 12:40 -0700
I had hoped to contribute to the recent discussion on William Bligh’s Navigation and Mapping, but the house was full of visitors, and I didn’t finish my intended input. However, whilst researching what Tables Requisite and Hamilton Moore’s might allow Bligh to do, I came across the following ex-meridian technique ‘Finding Latitude at Sea from Two Altitudes of the Sun and a Possibly Incorrect Watch’ (available in Google Books from P206 in the 1793 Tenth edition of Hamilton Moore’s and other places)
Now that really is sorcery (see my last post). Unfortunately Mr HM only tells you what to do, not why it works. I have four questions.
Is latitude by account the 18th Century name for DR latitude?
Is the index of a logarithm the bit before the decimal point?
Would the relevant technique be in earlier editions of Hamilton Moore, which Bligh is supposed to have had?
Please will one of you maths/geometry wizards explain why it works? If you don’t fancy using formulae and diagrams in WORD, a photo of freehand work will do.
Finally, I think it was Mr Fryer who said that when ashore during the longboat journey, Bligh didn’t help much but spent a lot of time sitting thinking. I thought this was a sign of a great delegator, something Bligh wasn’t particularly famed for, but perhaps he was just pondering over some of more esoteric concepts in Hamilton Moore. DaveP