[time-nuts] Measuring speed of light or reproducing a metre

[jmfranke]

Cool, thanks! Makes one wonder when the accuracy measuring time interval or 
frequency was finally better than the accuracy measuring distance.

John  WA4WDL

--------------------------------------------------
From: "Jim Lux" <jimlux at earthlink.net>
Sent: Monday, June 24, 2013 9:02 PM
To: <time-nuts at febo.com>
Subject: Re: [time-nuts] Measuring speed of light or reproducing a metre

> On 6/24/13 4:16 PM, jmfranke wrote:
>> The tuning fork was used with a clock. The clock was checked against
>> astronomical measurements.
>>
>> http://www.schoolphysics.co.uk/age16-19/Wave%20properties/Wave%20properties/text/Speed_of%20light/index.html
>>
>>
>> http://www.nhn.ou.edu/~johnson/Education/Juniorlab/C_Speed/2007-PhysToday-RefFrame-Michelson.pdf
>>
>>
>> http://www.loc.gov/item/magbellbib002940 synchronizing two forks, letter
>> to Bell.
>>
>> http://www.otherhand.org/home-page/physics/historical-speed-of-light-measurements-in-southern-california/the-mount-wilson-station-1922-1928/
>>
> excellent.. and I found on one of those pages the link to the US Geodetic 
> Survey information
> http://www.otherhand.org/wp-content/uploads/2012/03/A-Geodetic-Measurement-Of-Unusually-High-Accuracy.pdf
>
> The "Pasadena" baseline was almost as long as the 22 mile measurement, and 
> stretched from Pasadena to the east (San Dimas, etc.)
>
> I like the comment that direct measurement of the baseline to 1 part in 
> 500,000 wasn't considered particularly challenging ("routine"), but 
> transferring that measurement to the "MICHELSON" "ANTONIO" path was 
> challenging.
>
> Sure.. a few inches in 20 miles isn't particularly challenging...
> They measured it with 4 different tapes and came up only 18mm difference 
> among the measurements. That's some careful chaining. They were using 50 
> meter invar tapes: that means they had to put that tape out, pull it 
> straight to the rated tension, etc. about 700 times along the path.
>
> A great picture of the tape going through a house along the baseline, in 
> one window and out another.
> Ultimately, they measured the baseline (down on the flats) to 1 part in 
> 11.6 million, and they estimate the probable error of the 
> MICHELSON-ANTONIO line was 1 part in 5 million.
>
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