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Responding to Andres Ruiz' question about circles of reflection, I had 
written-

"I've read an account in English, by Mendoza about his improved circle, with 
a beautiful engraving, but can't now lay hands on it."

Discussing the matter with my friend and near-neighbour, Navlist member 
Clive Sutherland (who has built a reflection circle of his own) , Clive 
points out that the paper I couldn't locate was indeed one of those referred 
to by Andres himself in his original posting, as follows-


On an improved Reflecting Circle. Mendoza y R�os.
http://rstl.royalsocietypublishing.org/content/91/363.full.pdf+html

Here are a few assorted comments about that paper.

1. It's pleasing to note that the Royal Society is again providing copies of 
its historical papers free of charge. Normally, they are only available 
rather expensively, through Jstor. I don't know how long this will last.

2. Even for those that may have no technical interest in that paper itself, 
it's worth taking a look at the quality of the engravings. Unfortunately, to 
maintain the resolution, the copying process has required that they be split 
up a bit. Nevertheless, to my mind they compete with any work-of-art as 
things of beauty. Is that just my odd mind? What do others think?

3. Mendoza makes a comparison of his circle with its predecessors. Measuring 
with a circle always involved alternating between different observations. 
Each pair of such observations gave rise to an angle reading of 1 lunar 
distance on the Mayer circle. Borda saw that the instrument could be adapted 
to make a different observation sequence possible, such that each pair 
inreased the reading by 2 lunar distances. Mendoza, by introducing his 
clever "flying nonius", arranged that the overall measured angle increased 
by 4 lunar distances for each observation-pair.

contact George Huxtable, at  george@hux.me.uk
or at +44 1865 820222 (from UK, 01865 820222)
or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. 


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