A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Lars Bergman
Date: 2017 Feb 9, 14:41 -0800
Robin, et al,
There is one logarithm that indicates that Worsley is using a 6-figure table, but rounding to five figures. That is the last observation on May 7th, where log cos 85°41' is given as 876.62. In a 6-figure table, like Norie's Epitome of 1860, the log is given as 8.876615, which very well could be rounded up to 8.87662. In a 5-figure table it should be given as 8.87661. This is the only instance that I have found with this indication; in two other occasions rounding up of a "five" in the sixth decimal gives correct 5-figure result.
In Norie's Epitome of 1860, there is a 5-figure "Logarithms for finding the Apparent Time or Horary Angle" that, for the "rating" sight of April 24th, with interpolation, gives the time 2h55m25s before noon, or 21h4m35s astronomical time. Using more digits, log sin2(t/2)=9.14437 gives t=2h55m24s. But any 5-figure table would give the same result, so this is no proof ...
This Epitome, the 17th edition of 1860, is the only one that I can find on line.
It gives "Elephant or Barrow's I. - Cape Valentine" as 61°5'0"S, 54°55'0"W.
Finally, a minor remark: On 29th April there is an entry 57s, which most probably shall be read as 57°.