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From: hoey@nrl-aic.ARPA
Newsgroups: sci.physics
Subject: Speed of light
Message-ID: <252@sri-arpa.ARPA>
Date: Mon, 17-Nov-86 16:10:14 EST
Article-I.D.: sri-arpa.252
Posted: Mon Nov 17 16:10:14 1986
Date-Received: Tue, 18-Nov-86 21:22:02 EST
Lines: 38

From:  Dan Hoey <hoey@nrl-aic.ARPA>

    Date: Thu,  6 Nov 86 23:57:34 EST
    From: "Keith F. Lynch" <KFL@MX.LCS.MIT.EDU>

    ...
      Since 1982 the length of the meter (and hence of the inch, mile, etc)
    has been defined in terms of the length of the second and the speed of
    light.  This means that the speed of light is now constant by
    definition.  This also means that since 1982, nobody has measured the
    speed of light.  Anyone who thought he was doing so was actually
    measuring the length of the meter!
								...Keith

As I recall, the definition is chosen so as to make the speed of light
an integral number of meters per second.  Do you know the number?
Also, I have heard that the integral number of m/s applies only at some
experimentally convenient ultralow pressure, and that the speed in
vacuum is still subject to errors in measurement of refractive index.
Can you corroborate or debunk this?

I mostly want the value to make an accurate not-just-a-good-idea-it's-
the-law (or my-limits) bumper sticker or button for a change.  The
common approximation of 186000 mi/s is galling, since so many people
take it for scripture.

Speaking of scripture, my grandfather was into biblical numerology (for
lack of a better term).  He took a phrase about the light of heaven
being a thousand times that of the earth, and wrote a paper about the
length of heaven's light year and the number of square LY in heaven and
the like.  Of course he used 186000 mi/s and carried his results out to
dozens of figures.  What stupefied me was his use of a year composed of
24*365 + 12/4 hours.  This from a man who was alive in 1900!

And what cretin decided to metrify our speed limits into km/hr, anyway?

Dan Hoey
HOEY@NRL-AIC.ARPA