Mason and Dixon's Other Line 
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Richard
Posts: 8

Joined: 10/23/2008
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I have been doing some research on the arc of the meridian measured by the two surveyors between 1763-1768. A.H. Mason, the editor of the Mason-Dixon journals, writes that the southern component of the arc was "The meridional component of the Tangent Line
from the Tangent Point to the Middle Point." My reading of the journals and the paper presented to the Royal Society in 1768 leads me to believe that the southern segment of the arc was the meridional component of the first line run by the surveyors in 1764 from the Middle Point to Newcastle. The surveyors then laid out the Tangent Line by calculating offsets to this first line. They never actually measured the Tangent Line. Are there any M-D experts who can resolve this issue for me?
Richard
  Tuesday, December 09, 2008 at 5:27:25 PM
Will
Posts: 14
Location: Allentown, PA USA

Joined: 10/21/2008
Reply  Re: Mason and Dixon's Other Line Flag »  Reply »
I don't have the answer. But I have collected virtually everything written about Mason and Dixon, and will forward an article I wrote years ago for presentation at the SHS conference in Gettysburg. The answer may lie in one of the references. My email adress: wilhelms@nni.com.
  Wednesday, December 17, 2008 at 4:18:30 PM
Richard
Posts: 8

Joined: 10/23/2008
Reply  Re: Mason and Dixon's Other Line Flag »  Reply »
Thanks for the response. I am looking forward to finding out about the sources I don't have--yet!
  Saturday, December 27, 2008 at 7:54:19 PM
jwahl
Posts: 8

Joined: 1/31/2009
Reply  Re: Mason and Dixon's Other Line Flag »  Reply »
What follows is some stuff about the actual boundary line and after I wrote it I realized you were talking about the line they ran to measure 'the length of a degree of latitude'.

It looks to me from journal entries on pages prior to and after page 146 that they made extensive observations to determine an astronomic meridian. They note offsets to their first line and to the colonial meridian line.  They then packed up. So can I guess they were merely doing a precise check on their previous line and used it instead?  Well I think all the info is there if you can wade through it and put it together in the right order.

There are several thorough books besides the journals which tell you pretty much everything if you study them diligently.  There is a recent book that is mostly okay "Drawing the Line" by Danson. 

One excellent historical description of the entire background is contained in the published reports of the Resurvey Commission completed in 1907. The history is rather exhaustive and complete as I recall. It was written by a E. B. Mathews. There are versions of this report published by Maryland and by PA.  That book may be available online at google books or other sites on line.  The Mason and Dixon transcript journal publication is now on line also.

To bore you with what I wrote on the tangent line, here it is.

My recollection is that Mason and Dixon reran the colonial surveyors 3rd line or started in that direction and then noted offsets from it as they went. At the completeion they computed offsets and corrected direction for the line every 5 miles going back down to the middle point. At the 10 mile point they set up a line to the north and south to test their offsets and ran a line down to the middle point taking small offsets to the first line. 2 feet 2" back at the middle point.  They went back up the the 10 mile trial line they had laid out from their offsets and ran a new line back northward noting small offsets with their line first run. missing the tangent point by 16 feet.  (so that is twice they have run the line).

Page 65 describes what they then computed from that data. They had two lines run and two sets of offsets which they compared and they were generally less than two feet different.

The colonial surveyors first ran a meridian from the middle point eventually intersecting a radial from Newcastle and measuring the angle they computed a correction to try to run back up to tangent.  In 1862 they then started to run the first actual attempt at the tangent line checked by offsets from their meridian line but they came in almost 34 chains east of the expected tangent point.  They eventually went back and corrected and reran the line again and now missed the circle by over 5 chains to the west.

I think this was pretty frustrating to them and by that time Mason and Dixon had been contracted to finish the work.

One problem with the published transcript journals is that they are not completely organized chronologically and there are some typos.

I should review this to make sure my recollections match the facts.  My recollection is that they came back later to make the final tweak offsets and set the monuments.  Also they at least chained this line again for the degree of latitude work which was done with different equipment.

- jlw
  Friday, February 27, 2009 at 10:40:22 PM

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