> But would anyone claim to measure declination to
> seconds of arc?
Hmmm. That's one reason why I hesitated to make
the suggestion but there are three tiny points to
note:
1. The meridian line in the Basilica di S. Maria
degli Angeli in Rome was laid down in 1702 and
that IS true north-south to within a few seconds
of arc so it could be done in 1845.
2. In 1845 measuring longitude to seconds of arc
probably wouldn't have been significantly
easier than measuring declination to seconds
of arc.
3. The quoted angle is 35 deg. 43 min. 40 sec.
That could be interpreted as "measuring to the
nearest third of an arc-minute" which doesn't
sound quite so challenging.
The use of Position Lines in navigation is attributed
to Thomas Sumner in 1837. There must be readers of
this list who know how things developed from then.
It is conceivable that by 1845 the idea was well known
to navigators and others. Writing PL on your sundial
might be a way of showing that you were using modern
ideas!
OK. I'm clutching at straws!
Incidentally, this quoted figure for longitude is within
a few arc-minutes of being the co-latitude. Weird!
Frank King
Cambridge, U.K.
---------------------------------------------------
https://lists.uni-koeln.de/mailman/listinfo/sundial
