OT: Length of the Meter?

[Bill Bowden]

I read the current definition of a meter is the distance light travels in
1/299,792,358 of a second. How did they come up with a number like that? Why
not just call it 1/300,000,000? I also read the meter is 1/10,000,000th the
distance from the north pole to the equator. How was that measured so
accurately?



--- news://freenews.netfront.net/ - complaints: news@netfront.net ---

 

The one about the equator and pole is the original one and was derived geometrically. That's right, when they told us people thought the world was flat they lied. (you have to go pretty far back for that, alot farther than like the 1400s, the only people on the Nina, Pinta and Santa Maria who thought they would sail off the edge of the Earth were totally uneducated)

The one about the light is just a contemporary equivalent, measured to the original. It's just an easier way NOW to do it.

Same way with a second. There were latitudes, hours, minutes and then seconds. Now they say it is so many vibrations of the cesium atom or something like that, but that is a contemporary thing. It is just easier NOW.

It's also interesting how they figured out ohms, volts and amperes. Wiki should have a good article on all that, including your original question.

 

"Not just any ten-millionth, but a ten-millionth of the quarter-meridian
passing through _Paris_. Pure Greenwich envy. "

Are they STILL sticking their middle fingers out at each other ? (you DO know that story right ?)

"despite the fact that both ends of
that line are at sea. The idea promptly sank as a result "

How come that became the number five ? Did they try it five times ? They also can't spell. "cinq" ? Worse than Spanish.

" (And by the way it's
1/299,792,458.) "

Is that why that neutrino apparently went faster than the speed of light ?

http://www.reuters.com/article/2011/09/22/us-science-light-idUSTRE78L4FH20110922

 

[Michael Black]

On Thu, 15 May 2014, Bill Bowden wrote:

I read the current definition of a meter is the distance light travels in
1/299,792,358 of a second. How did they come up with a number like that? Why
not just call it 1/300,000,000? I also read the meter is 1/10,000,000th the
distance from the north pole to the equator. How was that measured so
accurately?

The length of the meter is however big you choose it. It could be some
tiny meter with barely a scale, for a tuning indicator in a stereo
receiver, or it could be nice and big, the meter in my Senior Voltohmyst
VTVM.

As for a metre, everyone knows it's 39.37 inches long.


As for your question, it has to be based on some reality, not a random
even number.

Michael

 

[Phil Hobbs]

On 5/15/2014 9:23 PM, Bill Bowden wrote:

I read the current definition of a meter is the distance light travels in
1/299,792,358 of a second. How did they come up with a number like that? Why
not just call it 1/300,000,000? I also read the meter is 1/10,000,000th the
distance from the north pole to the equator. How was that measured so
accurately?

Not just any ten-millionth, but a ten-millionth of the quarter-meridian
passing through _Paris_. Pure Greenwich envy.

Soon after their Revolution, the French defined the metre that way, and
dispatched surveyors to measure it, despite the fact that both ends of
that line are at sea. The idea promptly sank as a result (like so many
subsequent French initiatives).

More recently, even the SI folks have abandoned the guillotine and tried
to reduce the impact of redefinitions on pre-existing equipment and
scientific results. So when time and frequency became more accurate
than any mechanical measurement, the definition of the metre was
switched over to time and frequency. (And by the way it's
1/299,792,458.)

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

[John Larkin]

On Thu, 15 May 2014 20:03:51 -0700 (PDT), jurb6006@gmail.com wrote:

"Not just any ten-millionth, but a ten-millionth of the quarter-meridian
passing through _Paris_. Pure Greenwich envy. "

Are they STILL sticking their middle fingers out at each other ? (you DO know that story right ?)

"despite the fact that both ends of
that line are at sea. The idea promptly sank as a result "

How come that became the number five ? Did they try it five times ? They also can't spell. "cinq" ? Worse than Spanish.

" (And by the way it's
1/299,792,458.) "

Is that why that neutrino apparently went faster than the speed of light ?

http://www.reuters.com/article/2011/09/22/us-science-light-idUSTRE78L4FH20110922

I think they did something stupid with a cable in their test gear. You'd think
they would check stuff like that before they went public.




--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation

 

[John Larkin]

On Thu, 15 May 2014 22:52:24 -0400, Phil Hobbs <hobbs@electrooptical.net> wrote:

On 5/15/2014 9:23 PM, Bill Bowden wrote:
I read the current definition of a meter is the distance light travels in
1/299,792,358 of a second. How did they come up with a number like that? Why
not just call it 1/300,000,000? I also read the meter is 1/10,000,000th the
distance from the north pole to the equator. How was that measured so
accurately?

Not just any ten-millionth, but a ten-millionth of the quarter-meridian
passing through _Paris_. Pure Greenwich envy.

But they didn't specify the time of the day/month/year to make the measurement.


--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation

 

[Phil Hobbs]

On 05/15/2014 11:03 PM, jurb6006@gmail.com wrote:

"Not just any ten-millionth, but a ten-millionth of the quarter-meridian
passing through _Paris_. Pure Greenwich envy. "

Are they STILL sticking their middle fingers out at each other ? (you DO know that story right ?)

"despite the fact that both ends of
that line are at sea. The idea promptly sank as a result "

How come that became the number five ? Did they try it five times ? They also can't spell. "cinq" ? Worse than Spanish.

Robespierre & Co took a bit of discouraging, I suppose.

Cheers

Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

[Bill Bowden]

"Phil Hobbs" <hobbs@electrooptical.net> wrote in message
news:53757D68.9090204@electrooptical.net...

On 5/15/2014 9:23 PM, Bill Bowden wrote:
I read the current definition of a meter is the distance light travels in
1/299,792,358 of a second. How did they come up with a number like that?
Why
not just call it 1/300,000,000? I also read the meter is 1/10,000,000th
the
distance from the north pole to the equator. How was that measured so
accurately?

Not just any ten-millionth, but a ten-millionth of the quarter-meridian
passing through _Paris_. Pure Greenwich envy.

Soon after their Revolution, the French defined the metre that way, and
dispatched surveyors to measure it, despite the fact that both ends of
that line are at sea. The idea promptly sank as a result (like so many
subsequent French initiatives).

More recently, even the SI folks have abandoned the guillotine and tried
to reduce the impact of redefinitions on pre-existing equipment and
scientific results. So when time and frequency became more accurate than
any mechanical measurement, the definition of the metre was switched over
to time and frequency. (And by the way it's 1/299,792,458.)

Cheers

Phil Hobbs

Yes, I understand it was switched from the physical length of a metal bar to
the accuracy of a cesium clock and speed of light. But I'm still curious how
the length of the metal bar was measured to within 1 part in 300,000,000?

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

--- news://freenews.netfront.net/ - complaints: news@netfront.net ---

 

[Phil Hobbs]

On 5/16/2014 7:54 PM, Bill Bowden wrote:

"Phil Hobbs" <hobbs@electrooptical.net> wrote in message
news:53757D68.9090204@electrooptical.net...
On 5/15/2014 9:23 PM, Bill Bowden wrote:
I read the current definition of a meter is the distance light travels in
1/299,792,358 of a second. How did they come up with a number like that?
Why
not just call it 1/300,000,000? I also read the meter is 1/10,000,000th
the
distance from the north pole to the equator. How was that measured so
accurately?

Not just any ten-millionth, but a ten-millionth of the quarter-meridian
passing through _Paris_. Pure Greenwich envy.

Soon after their Revolution, the French defined the metre that way, and
dispatched surveyors to measure it, despite the fact that both ends of
that line are at sea. The idea promptly sank as a result (like so many
subsequent French initiatives).

More recently, even the SI folks have abandoned the guillotine and tried
to reduce the impact of redefinitions on pre-existing equipment and
scientific results. So when time and frequency became more accurate than
any mechanical measurement, the definition of the metre was switched over
to time and frequency. (And by the way it's 1/299,792,458.)

Cheers

Phil Hobbs


Yes, I understand it was switched from the physical length of a metal bar to
the accuracy of a cesium clock and speed of light. But I'm still curious how
the length of the metal bar was measured to within 1 part in 300,000,000?

Interferometry of one sort or another, I think. A Michelson
interferometer using a He-Ne laser will give you 2m/632.8 nm = 2.8
million cycles per metre. Not too high a SNR required to get to 1 part
in 300,000,00 from there, assuming you know where you start from.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

[John Larkin]

On Fri, 16 May 2014 16:54:08 -0700, "Bill Bowden"
<bperryb@bowdenshobbycircuits.info> wrote:

"Phil Hobbs" <hobbs@electrooptical.net> wrote in message
news:53757D68.9090204@electrooptical.net...
On 5/15/2014 9:23 PM, Bill Bowden wrote:
I read the current definition of a meter is the distance light travels in
1/299,792,358 of a second. How did they come up with a number like that?
Why
not just call it 1/300,000,000? I also read the meter is 1/10,000,000th
the
distance from the north pole to the equator. How was that measured so
accurately?

Not just any ten-millionth, but a ten-millionth of the quarter-meridian
passing through _Paris_. Pure Greenwich envy.

Soon after their Revolution, the French defined the metre that way, and
dispatched surveyors to measure it, despite the fact that both ends of
that line are at sea. The idea promptly sank as a result (like so many
subsequent French initiatives).

More recently, even the SI folks have abandoned the guillotine and tried
to reduce the impact of redefinitions on pre-existing equipment and
scientific results. So when time and frequency became more accurate than
any mechanical measurement, the definition of the metre was switched over
to time and frequency. (And by the way it's 1/299,792,458.)

Cheers

Phil Hobbs


Yes, I understand it was switched from the physical length of a metal bar to
the accuracy of a cesium clock and speed of light. But I'm still curious how
the length of the metal bar was measured to within 1 part in 300,000,000?

It probably wasn't, any more than the pole-to-equator distance was
measured to PPB accuracy. I suspect they did their best and moved on.



--

John Larkin Highland Technology, Inc

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

On Thu, 15 May 2014 18:23:09 -0700, "Bill Bowden"
<bperryb@bowdenshobbycircuits.info> wrote:

I read the current definition of a meter is the distance light travels in
1/299,792,358 of a second. How did they come up with a number like that? Why
not just call it 1/300,000,000? I also read the meter is 1/10,000,000th the
distance from the north pole to the equator. How was that measured so
accurately?



--- news://freenews.netfront.net/ - complaints: news@netfront.net ---

Speaking of measurement standards and such good clocks are needed to
make good length standards by measuring how far light travels in a
certain amount of time. Accuracy of the timekeeping limits accuracy of
length. Resolution is important too, the goal being to get smaller and
smaller parts per part. And of course the rate of time passing has to
be kept track of since it changes depending on the clock's distance to
massive objects, like planets. As we all know the closer to massive
objects we are the slower time passes. So those folks living in sky
scraper penthouses may have a better view but pay for it in shorter
lives compared to those living on the ground floor. At this time (pun
intended) we can measure elevation changes by comparing how fast
clokcs tick. Or resonate. Or whatever. In fact, GPS isn't very
accurate unless we account for the satellite speed (which slows time)
and the distance from Earth (which speeds time up). But we can measure
smaller elevation differences than the mean distance a satellite is
from Earth by measuring the rate of time passing. In fact, we can
measure elevation differences of less than 3 feet by observing the
difference in time passing. So if you take your atomic clock off the
bench and set it on the floor to make room for your death ray
prototype, you had better account for the time difference so that your
GPS pointing device makes your death ray take out that nerd who is
vying for your job and not his babe secretary.
Eric

 

[Phil Allison]

"Michael Black"

As for a metre, everyone knows it's 39.37 inches long.

** Since 1959 the inch and the yard are defined in terms of the metre.

1 inch = 25.4mm exactly

1 yard = 0.9144 metres exactly





..... Phil

 

[Phil Hobbs]

On 5/16/2014 8:45 PM, Phil Allison wrote:

"Michael Black"


As for a metre, everyone knows it's 39.37 inches long.


** Since 1959 the inch and the yard are defined in terms of the metre.

1 inch = 25.4mm exactly

1 yard = 0.9144 metres exactly

Absolutely, we should recognize other folks' hard work.

Of course 200 years ago, the English used to capture more French (and
especially Spanish) ships than they built themselves.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

[Bill Bowden]

"John Larkin" <jlarkin@highlandtechnology.com> wrote in message
news:nebdn99iq0v6qdush0rmv7ivuungh26kov@4ax.com...

On Fri, 16 May 2014 16:54:08 -0700, "Bill Bowden"
bperryb@bowdenshobbycircuits.info> wrote:


"Phil Hobbs" <hobbs@electrooptical.net> wrote in message
news:53757D68.9090204@electrooptical.net...
On 5/15/2014 9:23 PM, Bill Bowden wrote:
I read the current definition of a meter is the distance light travels
in
1/299,792,358 of a second. How did they come up with a number like
that?
Why
not just call it 1/300,000,000? I also read the meter is 1/10,000,000th
the
distance from the north pole to the equator. How was that measured so
accurately?

Not just any ten-millionth, but a ten-millionth of the quarter-meridian
passing through _Paris_. Pure Greenwich envy.

Soon after their Revolution, the French defined the metre that way, and
dispatched surveyors to measure it, despite the fact that both ends of
that line are at sea. The idea promptly sank as a result (like so many
subsequent French initiatives).

More recently, even the SI folks have abandoned the guillotine and tried
to reduce the impact of redefinitions on pre-existing equipment and
scientific results. So when time and frequency became more accurate
than
any mechanical measurement, the definition of the metre was switched
over
to time and frequency. (And by the way it's 1/299,792,458.)

Cheers

Phil Hobbs


Yes, I understand it was switched from the physical length of a metal bar
to
the accuracy of a cesium clock and speed of light. But I'm still curious
how
the length of the metal bar was measured to within 1 part in 300,000,000?

It probably wasn't, any more than the pole-to-equator distance was
measured to PPB accuracy. I suspect they did their best and moved on.

Yes, they probably ran the test 1000 times and averaged it out.




--- news://freenews.netfront.net/ - complaints: news@netfront.net ---

 

[Phil Hobbs]

On 05/16/2014 08:33 PM, John Larkin wrote:

On Fri, 16 May 2014 16:54:08 -0700, "Bill Bowden"
bperryb@bowdenshobbycircuits.info> wrote:


"Phil Hobbs" <hobbs@electrooptical.net> wrote in message
news:53757D68.9090204@electrooptical.net...
On 5/15/2014 9:23 PM, Bill Bowden wrote:
I read the current definition of a meter is the distance light travels in
1/299,792,358 of a second. How did they come up with a number like that?
Why
not just call it 1/300,000,000? I also read the meter is 1/10,000,000th
the
distance from the north pole to the equator. How was that measured so
accurately?

Not just any ten-millionth, but a ten-millionth of the quarter-meridian
passing through _Paris_. Pure Greenwich envy.

Soon after their Revolution, the French defined the metre that way, and
dispatched surveyors to measure it, despite the fact that both ends of
that line are at sea. The idea promptly sank as a result (like so many
subsequent French initiatives).

More recently, even the SI folks have abandoned the guillotine and tried
to reduce the impact of redefinitions on pre-existing equipment and
scientific results. So when time and frequency became more accurate than
any mechanical measurement, the definition of the metre was switched over
to time and frequency. (And by the way it's 1/299,792,458.)

Cheers

Phil Hobbs


Yes, I understand it was switched from the physical length of a metal bar to
the accuracy of a cesium clock and speed of light. But I'm still curious how
the length of the metal bar was measured to within 1 part in 300,000,000?

It probably wasn't, any more than the pole-to-equator distance was
measured to PPB accuracy. I suspect they did their best and moved on.

I think it was more like 5-10 ppb at the time--ISTR one of the last
official measured values of c was 299792456.3 m/s, back in the early 70s
(when I was into memorizing stuff like that).

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

[John Larkin]

On Mon, 19 May 2014 07:48:37 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 05/16/2014 08:33 PM, John Larkin wrote:
On Fri, 16 May 2014 16:54:08 -0700, "Bill Bowden"
bperryb@bowdenshobbycircuits.info> wrote:


"Phil Hobbs" <hobbs@electrooptical.net> wrote in message
news:53757D68.9090204@electrooptical.net...
On 5/15/2014 9:23 PM, Bill Bowden wrote:
I read the current definition of a meter is the distance light travels in
1/299,792,358 of a second. How did they come up with a number like that?
Why
not just call it 1/300,000,000? I also read the meter is 1/10,000,000th
the
distance from the north pole to the equator. How was that measured so
accurately?

Not just any ten-millionth, but a ten-millionth of the quarter-meridian
passing through _Paris_. Pure Greenwich envy.

Soon after their Revolution, the French defined the metre that way, and
dispatched surveyors to measure it, despite the fact that both ends of
that line are at sea. The idea promptly sank as a result (like so many
subsequent French initiatives).

More recently, even the SI folks have abandoned the guillotine and tried
to reduce the impact of redefinitions on pre-existing equipment and
scientific results. So when time and frequency became more accurate than
any mechanical measurement, the definition of the metre was switched over
to time and frequency. (And by the way it's 1/299,792,458.)

Cheers

Phil Hobbs


Yes, I understand it was switched from the physical length of a metal bar to
the accuracy of a cesium clock and speed of light. But I'm still curious how
the length of the metal bar was measured to within 1 part in 300,000,000?

It probably wasn't, any more than the pole-to-equator distance was
measured to PPB accuracy. I suspect they did their best and moved on.

I think it was more like 5-10 ppb at the time--ISTR one of the last
official measured values of c was 299792456.3 m/s, back in the early 70s
(when I was into memorizing stuff like that).

Cheers

Phil Hobbs

The meter itself was two scratches on a platinum-iridium bar. I guess that could
be measured pretty well. One micron would be (...calculates furiously...) 1 PPM.
1 PPB might be optimistic.

https://en.wikipedia.org/wiki/Meter#Prototype_metre_bar



--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation

 

[Phil Hobbs]

On 05/19/2014 11:53 AM, John Larkin wrote:

On Mon, 19 May 2014 07:48:37 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 05/16/2014 08:33 PM, John Larkin wrote:
On Fri, 16 May 2014 16:54:08 -0700, "Bill Bowden"
bperryb@bowdenshobbycircuits.info> wrote:


"Phil Hobbs" <hobbs@electrooptical.net> wrote in message
news:53757D68.9090204@electrooptical.net...
On 5/15/2014 9:23 PM, Bill Bowden wrote:
I read the current definition of a meter is the distance light travels in
1/299,792,358 of a second. How did they come up with a number like that?
Why
not just call it 1/300,000,000? I also read the meter is 1/10,000,000th
the
distance from the north pole to the equator. How was that measured so
accurately?

Not just any ten-millionth, but a ten-millionth of the quarter-meridian
passing through _Paris_. Pure Greenwich envy.

Soon after their Revolution, the French defined the metre that way, and
dispatched surveyors to measure it, despite the fact that both ends of
that line are at sea. The idea promptly sank as a result (like so many
subsequent French initiatives).

More recently, even the SI folks have abandoned the guillotine and tried
to reduce the impact of redefinitions on pre-existing equipment and
scientific results. So when time and frequency became more accurate than
any mechanical measurement, the definition of the metre was switched over
to time and frequency. (And by the way it's 1/299,792,458.)

Cheers

Phil Hobbs


Yes, I understand it was switched from the physical length of a metal bar to
the accuracy of a cesium clock and speed of light. But I'm still curious how
the length of the metal bar was measured to within 1 part in 300,000,000?

It probably wasn't, any more than the pole-to-equator distance was
measured to PPB accuracy. I suspect they did their best and moved on.

I think it was more like 5-10 ppb at the time--ISTR one of the last
official measured values of c was 299792456.3 m/s, back in the early 70s
(when I was into memorizing stuff like that).

Cheers

Phil Hobbs

The meter itself was two scratches on a platinum-iridium bar. I guess that could
be measured pretty well. One micron would be (...calculates furiously...) 1 PPM.
1 PPB might be optimistic.

https://en.wikipedia.org/wiki/Meter#Prototype_metre_bar

I don't know how the scratches were made. You can make atomically sharp
scratches in some materials, but I imagine the parallelism error would
be more than a ppb.

There was probably a standard way of comparing metre standards, so if
you take the standard metre as the combination of the bar and the
method, it might be better than 0.1 ppm.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

[John Larkin]

On Mon, 19 May 2014 16:56:43 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 05/19/2014 11:53 AM, John Larkin wrote:
On Mon, 19 May 2014 07:48:37 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 05/16/2014 08:33 PM, John Larkin wrote:
On Fri, 16 May 2014 16:54:08 -0700, "Bill Bowden"
bperryb@bowdenshobbycircuits.info> wrote:


"Phil Hobbs" <hobbs@electrooptical.net> wrote in message
news:53757D68.9090204@electrooptical.net...
On 5/15/2014 9:23 PM, Bill Bowden wrote:
I read the current definition of a meter is the distance light travels in
1/299,792,358 of a second. How did they come up with a number like that?
Why
not just call it 1/300,000,000? I also read the meter is 1/10,000,000th
the
distance from the north pole to the equator. How was that measured so
accurately?

Not just any ten-millionth, but a ten-millionth of the quarter-meridian
passing through _Paris_. Pure Greenwich envy.

Soon after their Revolution, the French defined the metre that way, and
dispatched surveyors to measure it, despite the fact that both ends of
that line are at sea. The idea promptly sank as a result (like so many
subsequent French initiatives).

More recently, even the SI folks have abandoned the guillotine and tried
to reduce the impact of redefinitions on pre-existing equipment and
scientific results. So when time and frequency became more accurate than
any mechanical measurement, the definition of the metre was switched over
to time and frequency. (And by the way it's 1/299,792,458.)

Cheers

Phil Hobbs


Yes, I understand it was switched from the physical length of a metal bar to
the accuracy of a cesium clock and speed of light. But I'm still curious how
the length of the metal bar was measured to within 1 part in 300,000,000?

It probably wasn't, any more than the pole-to-equator distance was
measured to PPB accuracy. I suspect they did their best and moved on.

I think it was more like 5-10 ppb at the time--ISTR one of the last
official measured values of c was 299792456.3 m/s, back in the early 70s
(when I was into memorizing stuff like that).

Cheers

Phil Hobbs

The meter itself was two scratches on a platinum-iridium bar. I guess that could
be measured pretty well. One micron would be (...calculates furiously...) 1 PPM.
1 PPB might be optimistic.

https://en.wikipedia.org/wiki/Meter#Prototype_metre_bar

I don't know how the scratches were made. You can make atomically sharp
scratches in some materials, but I imagine the parallelism error would
be more than a ppb.

There was probably a standard way of comparing metre standards, so if
you take the standard metre as the combination of the bar and the
method, it might be better than 0.1 ppm.

Cheers

Phil Hobbs

The metre should have been how far light travels in 1 ns. Given how
arbitrary the pole-to-equator thing was, they could have made 1 metre
= 1 foot, or 1 yard, except that they were French.

Interesting that 1" is precisely 25.4 mm.




--

John Larkin Highland Technology, Inc

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Jasen Betts]

On 2014-05-19, John Larkin <jlarkin@highlandtechnology.com> wrote:

On Mon, 19 May 2014 16:56:43 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:


The metre should have been how far light travels in 1 ns. Given how
arbitrary the pole-to-equator thing was, they could have made 1 metre
= 1 foot, or 1 yard, except that they were French.

Interesting that 1" is precisely 25.4 mm.

The inch was changed to be precisely 25.4mm some time last century
previously it was about 25.400051mm in USA and about 25.399956mm in the
Brittish commnwealth. and previos to that different.
--
umop apisdn


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