BBC News Interviews David Thaler on Mason Dixon

On June 19, David Thaler was interviewed by the BBC for part of a documentary on the Mason Dixon survey of 1763-1767. The survey was the first geodetic survey in the New World and the most outstanding engineering and scientific achievement of its day. The documentary will run on BBC One in the fall.

The interview was filmed at the Maryland Historical Society in Baltimore, which has approximately 300 documents related to the legendary survey including: the original plat of survey signed and sealed by the 12 boundary commissioners, the original contract for the survey signed by Lord Baltimore and the Penns, as well as the actual bill for the survey.

Check out some photos below from the interview and a blog post written by David Thaler about his journey of discovery on the Mason Dixon survey:

Chris Jackson, a senior producer for the BBC, was driving near his home in Newcastle, England when he heard a song on the radio by Mark Knopfler, a famous British rock star, entitled “Sailing to Philadelphia” recorded as part of the album of the same name with James Taylor. Knopfler, a native of the northeast corner of England is wildly popular and his song “Local Hero” is played at the beginning of all Newcastle United football matches.

Sailing to Philadelphia begins:

I am Jeremiah Dixon

I am a Geordie boy …

Sailing to Philadelphia

To draw the line

A Mason-Dixon Line …

A Geordie, pronounced “jordy” is someone from the northeast of England and Jackson, a Geordie boy himself, was fascinated. He had of course heard of Mason and Dixon and their famous line in America, but didn’t know much about it and he was surprised to learn that Jeremiah Dixon was also a Geordie boy. Intrigued, he did some research and quickly learned that the Mason Dixon survey of what is now the Maryland/Pennsylvania/Delaware border, was the most outstanding engineering and scientific achievement of its time, the equivalent of the moon landing today. He decided to produce a documentary and on June 21, 2017, he came to the MdHS Library to visit its treasures and to interview local engineer, surveyor and former MdHS trustee, David S. Thaler, an expert on the Mason Dixon survey.

Thaler had been on quite a journey of discovery himself, which began for him at the MdHS in 2009. When he was an officer of the Society and chair of the Library Committee, he became aware of the fabulous Calvert papers in the Library’s collection. They include approximately 1,300 documents related to the Calvert family, about 300 of which concern the 80 year long boundary dispute between Maryland and Pennsylvania. In 2009, with Thaler’s encouragement, the MdHS mounted an exhibition of these treasures entitled, “Mason-Dixon and the Defining of America.”

When Thaler’s friend, surveyor Todd Babcock, heard about the exhibition, he sent a photo and said he thought this was the actual instrument used by Mason & Dixon. It was a picture of a curious object, a telescope on a trunnion axel, mounted on a tripod stand. It was displayed as a decorative object between two globes on a shelf in the rear of the Governors’ council chamber in Independence Hall, Philadelphia.

Thaler called the curator, who identified the object as the instrument used in the famous 1769 Transit of Venus observation. Thaler knew the Mason Dixon instrument had been made for the Penns by John Bird, the most famous instrument maker of the 18th century and another Geordie boy. Thaler asked if he could examine the instrument. When he did and turned the barrel over, he found John Bird’s signature engraved upon it.

A paper had been published stating that, along with everything else that might be of value to the enemy, the instrument had been hidden away from the British after Lord Howe’s occupation of Philadelphia in 1777 and was rediscovered 135 years later in 1912 under the floorboards in the bell tower of Independence Hall. While wildly romantic, the story was not accurate and Thaler was able to determine that the transit had actually been mounted in the window of the bell tower where it was used to determine noon to set the tower clock until time was standardized by the railroads in about 1886. Thaler was thus able to prove the transit’s provenance as the actual instrument used by Mason and Dixon in their iconic survey in America.

After the completion of the survey in 1767, the American Philosophical Society constructed an observatory behind Independence Hall from whose steps, with the Bird instrument stored behind him, Col. John Nixon of the Pennsylvania Committee of Safety first proclaimed the Declaration of Independence at noon on July 8, 1776. So the little transit is surely one of America’s most historic scientific instruments.

When it was rediscovered, it was in terrible condition. In addition to missing many parts, it was inoperable and was heavily corroded. Thaler ran a nationwide campaign to raise the funds to restore and conserve the instrument.

Fully restored, it was brought to the MdHS and unveiled in an event on October 8, 2015, where it was ceremonially donated as “A Gift to the Nation” from the surveyors and engineers of America.

The transit was returned to Independence Hall after the event at the MdHS where it can be viewed today in its restored splendor, properly interpreted, and in its place of honor back in the Governors’ council chamber.

The Mason-Dixon Documentary will run on BBC One this fall.

—David Thaler