[tz] St Andrews meridian in the 17th century

Paul Eggert eggert at cs.ucla.edu
Sun Oct 5 17:37:18 UTC 2014

Peter Ilieve wrote:

> http://www.bbc.co.uk/news/uk-scotland-29474850

I'm afraid the BBC piece is quite wrong.  It leads with "A Scottish astronomer 
and scientist is thought to have laid the first meridian line" but Gregory was 
definitely not the first.  A famous earlier example is the meridian line in the 
Basilica of San Petronio, Bologna, placed there in 1575-6 by the Italian 
astronomer Ignazio Danti and greatly improved in 1655-7 (and restored in 1695) 
by Cassini.  This was a working meridian line; among other things, Cassini used 
it to measure the diameter of the Sun, to verify Kepler's second law, and (more 
relevant for the tz database) to dispel doubts about whether the year 1700 
should be a leap year.

You can see a photo of part of the current version of that line here:


and there's some background here:


My guess is that Dr John Amson told the BBC reporter that Gregory's line was the 
first line that was so long (2.4 km) and accurate, and the reporter jumped to 
the incorrect conclusion that it was the the first line ever.

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