Jon Elson wrote:
> Ian Wilson wrote:
>
> > On 10:10 AM 6/03/2001 +1100, John Haddy said:
> > >By definition, 1 inch = 25.4mm exactly. This was standardised
> > >some decades ago.
> > Off topic a little...
> >
> > But the metre (and hence inch) are derived quantities (variables) so all
> > our footprints are totally useless! Do you hear - *useless*!
> >
> > The speed of light, c, is constant. Any improvements in the how fast light
> > travels does not affect the number in metres per second. The length of the
> > metre is changed instead. So there is no point in trying to design
> > footprints as the next time a physicist improves the estimate of c we have
> > to go back and update all out libraries.
>
> This is actually not true. The Metre is based on an exact number of
> wavelengths
> of the Neon emission line that is characteristic of the HeNe laser, somewhere
> around 637 nM, I think. So, the length of objects is not changed by speed
> of light measurements. And, the wavelength of the Neon atom will remain
> quite stable when measured properly.
>
> Jon
>
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Actually the Neon emission line is derived from a frequency and you get the
wavelength only by using the speed of light.
Heart
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