Hi,

On 11/13/2017 06:32 PM, Gregory Beat wrote:

There is a lovely article about the Dixon-Mason line and how they now
used GPS to measure it accurately. Turns out that Dixon-Mason measured
wrong, but not because they where hacks, they did it very accuratly with
the tools they had, but the mercury of their star-scope was not
completely flat due to gravitational pull from mountains, so when
correcting for that with now known data, they are very accurate with
what they had.

I think there was a thread about it some time back, but you should be
able to find it knowing what o search for.

I learned about what the whole issue was about from start.

Cheers,
Magnus

On 11/13/17 9:32 AM, Gregory Beat wrote:

Googling "cadastral survey" would be how you'd find out.

There's also a famous case of the border between New Mexico and Colorado
being crooked because of poor surveying, but the monuments define the
border not the words in the laws defining the border.
http://www.denverpost.com/2007/08/02/were-not-so-square-after-all/
https://supreme.justia.com/cases/federal/us/267/30/case.html

Same with the border between Utah and Colorado.

The increased use of GPS has made it trivial to go out and find a
particular position - but remember - it's the monument that controls the
location and boundary, not the coordinates.  My house sits on a lot
where the corners are defined relative to some physical monumentation (a
brass disk nailed to the sidewalk typically,with a dimple in the nail
head) - so as my house gradually drifts north a few cm/year, I don't
have to worry about the line shifting.

Sometimes this "tied to the monument" thing breaks down - and that's
what court cases are made of.

In any case, most of the state boundaries in the western United States
were done with astronomical measurements.  Probably using a chronometer
for time, as opposed to using lunar occultation of stars.

The Commissioner of the General Land Office employed Ehud N. Darling, a
surveyor and astronomer, to make this survey. He made the survey in
1868, and filed his field notes in the Land Office. In accordance with
his instructions, he adopted as the northeast corner of New Mexico a
stone monument that had been established by Capt. J. N. Macomb, an Army
Engineer, in 1859, to mark the intersection of the 37th parallel with
the 103d meridian, and, taking this as his beginning point, surveyed and
marked the line of the parallel, as determined by astronomical
observations and calculations for latitude, westwardly to the 109th
meridian, a distance of over 331 miles. ...

Several years later, the Commissioner of the General Land Office
employed John J. Major, a surveyor and astronomer, to survey and mark
the remaining portion of the southern boundary of the Territory of
Colorado, extending along the 37th parallel to the 102d meridian. Major
made this survey in 1874, and marked the line of the parallel between
the Macomb monument and that meridian. The field notes of this survey
were filed in the Land Office and approved by the Commissioner.

and so on over the next 20-30 years

This kind of surveying was hard work: hostile native americans attacking
survey parties, wildlife (lions, bears, etc.).  The wildlife problem
wasn't quite as bad as tigers eating surveyors in India doing the Great
Trigonometric Survey.

On Mon, Nov 13, 2017 at 12:32 PM, Gregory Beat w9gb@icloud.com wrote:

I think one nautical mile per second is a bit off:

86,400 sec/day
Earth's circumference at lat. 41 is about 16,200 nautical miles, so it's
about 16200/86400 or 0.187 mi/sec

There is an interesting book "Longitude by Wire" by Richard Stachurski that
describes efforts in the mid 19th century to improve the accuracy of
surveys and determine the precise position of North America relative to
Europe.

This culminated in the use of pulses on telegraph lines to transfer
observatory time to remote stations. With this technique, very careful
measurements, and mathematical advances they were able reduce the longitude
uncertainty to less than 10 feet.

--

--Jim Harman

Longitude by Wire  by Richard Stachurski :
from Professional Surveyor Magazine, November 2003.
http://fgg-web.fgg.uni-lj.si/~/mkuhar/pouk/SG/Seminar/Astronomska_navigacija/Astronomska_navigacija_zgodovina/Professional_Surveyor_Magazine-Longitude_By_Wire_The_American_Method-Nov03.pdf

Best, 73,  Pat Barthelow AA6EG
apol apolloeme@gmail.comloeme@gmail.com

"The most exciting phrase to hear in Science, the one that heraldsnew
discoveries,  is not "Eureka, I have found it!"    but:
"That's funny..."  ----Isaac Asimov

On Mon, Nov 13, 2017 at 11:39 AM, Jim Harman j99harman@gmail.com wrote: