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Re: [ATM] how many errors can you spot in this passage on Foucault?
Thanks Guy,
That was a fun intellectual exercise.
Best regards,
Francis
----- Original Message -----
From: "Guy Brandenburg" <gfbrandenburg@yahoo.com>
To: "Guy Brandenburg" <gfbrandenburg@yahoo.com>; "atmlist" <atm@atmlist.net>
Sent: Wednesday, December 26, 2007 9:20 PM
Subject: Re: [ATM] how many errors can you spot in this passage on Foucault?
> Some of the readers on this list found some of the errors, but here are a
> few others that were not found, or at least not yet reported on so far
>
> (1) Foucault did not claim that he invented the method of silvering glass.
> He gave credit to Liebig and Steinheil on that.
>
> (2) The only astronomical (sort-of) use of rear-reflecting mirrors
> anywhere near that time frame (that I know of) was the Mangin mirror, and
> neither Herschel nor the Earl of Rosse nor anybody else was using those
> for telescopes. Instead, they were used for searchlights.
>
> (3) Foucault's real innovations were in methods for testing the mirrors.
> He essentially invented what we call the Ronchi test today, among other
> things. [Bob May correctly points out that the Couder/Foucault numerical
> knife-edge test that we use today is a serious modification of Foucault's
> original knife-edge test.] However, Foucault really was the one, I think,
> who realized that you needed to produce a parabola, or something very
> close to it, if you wanted to produce good mirrors, and was the one wo
> figured out way to guarantee that.
>
> The author of that paragraph with SOO many errors was Amir Aczel, in the
> book "Pendulum: Leon Foucault and the Triumph of Science" which I got
> cheap at Daedalus books. I am generally astonished at the large number of
> errors that Aczel makes in every book that I have read of his. Why does he
> keep getting a pass on that? If nothing else, a science writer should get
> the facts right, no?
>
> PS if you look at my webpage, the first link is to a translation of
> Foucault's article.
>
> The points that several writers got right are:
>
> (1) Speculum metal mirrors were probably only 2 or 3 times as dense as
> glass.
>
> (2) The really huge disadvantage of speculum metal mirrors was not -
> despite what either Foucault or Aczel said - that they were too heavy or
> would 'collapse the telescope' (what a completely nutty idea), but that
> they didn't reflect very much, tarnished quickly, and once they tarnished,
> had to be polished and resurfaced in an extremely time-consuming manner
> that essentially meant that one was re-figuring the original mirror all
> over again. (Just imagine how many telescope mirrors would be in customary
> use today if you had to go through all of the laborious steps of figuring
> your mirror every 6 weeks!). With a glass mirror that had a chemically
> silvered and mechanically smoothed surface, the tarnished reflecting layer
> can be removed chemically as needed when it becomes not reflective enough,
> and a new reflective layer can be put on without changing the figure of
> the mirror in the slightest. But, as I said, this idea was not original
> with Foucault.
>
> (3) Azcel doesn't understand reflecting telescopes at all.
> Guy
>
>
>
> Guy Brandenburg <gfbrandenburg@yahoo.com> wrote: Boys and girls,
>
> How many factual and conceptual errors can you spot in this passage,
> written about Leon Foucault by a writer who is often considered to be one
> of the major science/math popularists of the day? (The spelling mistakes,
> if any, are all mine.)
>
> "Foucault's great discovery in the area of astronomical instrumentation
> was a method of silvering the mirrors for reflecting telescopes.
> Reflecting telescopes that had been made up to that time used bulky, heavy
> mirrors. This limited the potential size of these telescopes because the
> weight of the mirror could collapse the telescope. Foucault inaugurated a
> new method of applying a layer of silver directly to the front of the
> telescope's mirror, rather than a mercury amalgam that was typically
> applied to the back of the mirror. Foucault's telescopes built this way
> were lighter and of better light-gathering quality than earlier
> telescopes, as evidenced by their use today, a century and a half after
> his time."
>
>
>
>
> Guy Brandenburg, Washington, DC
> My home page on astronomy, mathematics, education:
> http://home.earthlink.net/~gfbranden/GFB_Home_Page.html
> or else
> http://tinyurl.com/r6fh2
>
> =============================
> "Education isn't rocket science. It's much, much harder."
> (Author unknown)
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