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Nicol�s de Hilster wrote- in response to my quoting Newton's description of 
the way his instrument was divided-

Of course Newton's words sounded challenging to me. If he really meant
that he had diagonal scales down to those values what would he have
made. When we study his drawing it becomes clear that he left space for
the diagonal scale. Assuming his drawing was more or less to scale ...

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But the problem is that you can't assume ANYTHING about that engraving. It 
WASN'T  Newton's drawing, which had been lost. It had been drawn by an 
artist for the Royal Society, and then engraved, long after Newton's death 
(and after Halley's). It had been drawn from the words of Newton's note. 
Newton gave the dimensions of the telescope (as three or four feet) but said 
nothing about the size of the brass plate. It was no more than the 
imagination of the artist (and then the engraver) that made the plate the 
same size as the telescope. We are free to interpret the words of Newton's 
today as we think best, just as the Royal Society artist was free in 1742. 
And if we think a brass plate of three or four feet across to be impossibly 
unwieldy (which it would be) then we can make it, say, half the length of 
the telescope, or whatever we choose. What I am saying is that the engraving 
that Nicolas is going by is not a document that has any authenticity in 
itself.

It may be, of course, that the original instrument still existed, and was 
available to be drawn, in 1742. But if it was, I am pretty sure we would 
have heard about it.

None of this detracts, much, from Nicolas' speculation about how it might 
have been divided.

George.

contact George Huxtable at george@huxtable.u-net.com
or at +44 1865 820222 (from UK, 01865 820222)
or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. 


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