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George Huxtable wrote:

>
> Therefore, the conclusion is that Halley had indeed carried and used
> Newton's two-mirrored instrument, to measure the altitudes on which those
> latitudes were based.

Your conclusion does not follow the facts.  I already stated - we know
an instrument was designed and we know Halley made accurate
measurements.  Nothing connects the two except the statement in the
Journal book.  The Journal book entry does not identify precisely what
instrument was shown, not does it identify when or on what voyages (if
any) Halley used it. It was written by a third person - which in legal
terms means - hearsay.  The Journal book entry is ambiguous and you
treat it as an absolute.  All I'm asking for is a piece of evidence to
clarify the link - some independent statement to verify the exact events
being referred to.  If you think that's excessive, you're just putting
your faith in beliefs and pretending they're facts.

> "If he did use lunar distances, it is often suggested that he used
> Newton's," [Often, by whom?]

You, for starters.  See comment below on sources.

> "If folks are saying "Halley used Newton's original instrument", then that
> means the statement is false" [Who was saying that?]

Unless you don't read your own posts, I'll point out that this is
exactly what you are saying.

> "Some suggest it was because Halley wasn't that familiar with Newton's
> instrument" [When challenged, on who were the "some", the reply was-  "In
> exactly which books did I read that - offhand I can't remember". ]

This is a forum - I'm not publishing a bloody paper on the topic here.
I don't have the sources on hand - I'd have to travel to a city to visit
a library to look up those sources again to find the stuff.  I didn't
take specific notes.

> Newton's note gave no dimensions for his plate, only for the telescope. So
> how does Mike infer that the plate was "huge", and called for shrinking
> down?

Nicolas has given us a perfectly valid interpretation of the diagram and
Newton's description of the original instrument to show that the scale
of the instrument in the drawing is consistent with the accuracy called
for by Newton.  Even if the plate was shrunk down - how much could it be
shrunk and still result in a usable instrument?  Take the transversal
spacing and shrink it to the minimum size one can reasonably expect an
instrument maker to be able to construct - how big is the plate?  If you
take it to 1/6 arc minute and 1 mm spacing, it's still a 15 inch plate
affixed to the end of a 4 foot scope.  That puts the index arm 48-15 =
33" away from the eyepiece.

Have you ever lifted a four-foot telescope?  Here's mine (homemade tube):


That brass tube, without optics, weighs a _lot_.  Sure it's got a 100mm
aperture, but even if you shrink it down to 50 or even 25 mm, that thing
is going to be too heavy to lift and use with any accuracy - even if it
only has 3x magnification (3' F.L. objective and 1' eyepiece F.L.).

I challenge anyone on this forum to make such a telescope, hold it at an
angle that reasonably represents normal use and, with one hand on the
scope, adjust the index to set the angle.  Even without a plate of any
size, you will not be able to do it - that would be a two-person
operation.  You can make the tube light if a big heavy plate supports
the scope, otherwise, you need a stiff tube to support the smaller plate.

Compared to a Davis Quadrant, there's no question a legitimate mariner
would reject Newton's proposal.  Which makes my statement to Nicolas
stand.  If he's right about the size - the case against the usability of
Newton's instrument is even stronger.

Mike




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