June 27, 2019

Epping Plains site of ambitious 1850s survey > Base line in Columbia one of 6 used to map eastern U.S.

It was foggy on the Epping Plains. Alexander Dallas Bache arrived at the base camp around 9 a.m., after traveling six miles over a bad road from Cherryfield.

Bache was superintendent of the U.S. Coast Survey, charged by Congress to map the Atlantic seaboard from Maine to Louisiana. The year was 1857.

Already, the project was entering its sixth decade. Shipping had increased dramatically since the American Revolution, but the accuracy of existing nautical charts was poor. Congress authorized the project in 1807 to aid in national defense and navigation.

Albert Gallatin, secretary of the treasury under Thomas Jefferson, asked leading scientists for proposals to map the nation’s coast accurately. A Swiss immigrant named Ferdinand Rudolph Hassler proposed a survey based on a chain of triangles stretching from mountaintop to mountaintop down the Appalachians.

Known as the Eastern Oblique Arc, the chain would serve as the framework for linking individual harbor surveys. It was an ambitious proposal, a major scientific undertaking at a time when geodetic surveying was in its infancy.

Unlike property surveys, used to establish the bounds of a parcel of land, geodetic surveys determine the absolute position of points on the Earth.

“(In the 1800s) the United States was at the leading edge of this technology,” said Harold E. Nelson of Newport, who has studied the coastal survey for more than a decade. A thick stack of documents compiled by Nelson was used to prepare this article.

A look at the theory

The chain of triangles proposed by Hassler was based on six lines, measured with extreme accuracy, spaced at irregular intervals from southwest Alabama to eastern Maine. The lengths of the six base lines would be used to calculate the sides of triangles in the chain.

Any error in measuring the six lines would be compounded by the mathematical calculations used to create the Eastern Oblique Arc. Such errors ultimately would reduce the accuracy of the coastal survey.

Hassler died before the project could be completed. In 1843, he was succeeded by Bache, a great-grandson of Benjamin Franklin.

To measure the base lines with the greatest possible accuracy, Bache and an assistant created the Bache-Wurdemann Compensation Base Apparatus.

The device consisted of two bars, brass and iron, bolted solidly together at one end. At the other end, the bars were connected by a “lever of compensation.” The lever allowed the bars to expand and contract with temperature changes, but kept the ends of the device a constant six meters apart. The entire apparatus was encased in a double-walled tin tube, and the tube was supported by trestles.

Epping is measured

Bache and his surveying team came to Maine in 1853. While Bache worked at Mount Blue and Sabbatus Mountain, he sent two assistants to eastern Maine to find a suitable spot for the northernmost of the six base lines.

The lines usually were put on open beaches. But the rugged Maine coast forced Charles O. Boutelle and Maj. Henry Prince to look inland. They chose the Epping Plains in Columbia, which they described as a large pine barren of rolling sand ridges covered with grass and brush, and scattered patches of woods. They made no mention of wild blueberries.

Prince returned in 1854, made a rough survey of the plain and decided that a straight line of five or six miles could be measured. The next year, Boutelle made a survey of elevations along the proposed base line.

Bache inspected and approved the site in 1856. The line was cleared and four towers were erected along it. The towers would be used to ensure the surveyors measured a line that was perfectly straight.

In May 1857, local farmers and lumbermen were hired to grade a 12-foot-wide path along the proposed line. Where necessary, the path was cut into banks or raised by stone cribbing so that the incline or decline never exceeded one foot in six meters.

Bache arrived on the morning of July 15, 1857, to oversee the measurement of the base line. It was foggy on the Epping Plains, and it would remain foggy and rainy for most of the next two weeks.

A survey crew of about 22 people unpacked two Bache-Wurdemann devices. The plan was to set the near end of the first tube directly over a mark on the western end of the base line, which was located on a granite outcropping in Deblois. After the first tube was aligned directly toward the eastern end of the base line, the second tube would be brought into contact with it.

The measurement would proceed six meters at a time, as the crew leapfrogged the Bache-Wurdemann devices over the entire 5.4 miles of the Epping Base Line. Where the line was not perfectly level, the surveyors would note the angle of inclination and later adjust the measured distance.

The crew made little progress until July 27, when the weather finally broke. Over the next eight days (with a rest on Sunday, Aug. 2) they measured 1,453 tubes plus a fraction. When conditions were good, a tube could be set in as little as two minutes.

The measurement was completed Aug. 4, and monuments of Italian marble were set at each end of the Epping Base Line. Bache left Aug. 7 and most of the crew were paid off.

Jefferson Davis comes calling

When Bache returned to Maine the next year, an old friend and benefactor came to visit him. Jefferson Davis, the Virginia senator who later became president of the Confederacy, called on Bache at his surveying camp on Lead Mountain near Beddington.

The visit by Davis gave rise to a local legend that Davis stayed at an inn on Shoppe Hill in Cherryfield. Davis reportedly left a trunk there with instructions that someone would pick it up later.

Legend has it that a stranger came in the night, gave a password and took the trunk, which was rumored to contain plans for the Civil War. There is no evidence that the story is true.

In any case, Bache and his work gradually were forgotten. Vandals defaced the marble monuments. Everything except the Base Line Road and the legend of Jefferson Davis faded into obscurity. The other five base lines — in Massachusetts, New York, Maryland, Georgia and Alabama — disappeared.

A few people remember

Only a few local surveyors knew the location or significance of Epping. One of them was Blair Riopell of Machias, a surveyor for the Maine Department of Transportation.

Riopell’s stories about the base line fired the imagination of Nelson, one of his co-workers. In 1980, Nelson visited the broken marble monument at the western end of the base line. He spent the next 11 years researching Epping and the coast survey.

According to Nelson, there was no written documentation in Maine — only tales told by people who lived on the barrens. The search took him to the offices of the National Geodetic Survey in Washington, D.C.

“All kids like to go on a treasure hunt,” Nelson said in describing his research.

Calculations made in the mid-1800s from the base line at Fire Island, N.Y., had showed that Bache measured the Epping Base Line within 2 inches of its actual length. Nelson interested the Maine Society of Land Surveyors in a plan to check the accuracy of Bache’s work using modern surveying technology.

“The Epping Base Line is the only one of the six that can still be measured,” he said. “The others are missing, washed out to sea or buried.”

Epping measured again

Stevenson W. Shepard of the James Sewall Co. in Old Town was appointed chairman of the society’s Epping Base Line committee. He enlisted the help of co-worker Bruce Barry, who formulated a plan to measure the line using the Global Positioning System.

GPS relies on signals from a network of 16 satellites orbiting the Earth at high altitudes. By measuring the distances from several of the orbiting satellites, the system can determine precisely the location of points on the Earth.

Nelson said the technology relies on the same principles that guided Bache.

“All surveying is based on the same premise,” he said. “If you know the length of one side of a triangle and two angles, you can calculate the other angle and the length of the two unknown sides.”

The Department of Defense is spending $10 billion to develop GPS. The system proved its worth (and accuracy) during the Persian Gulf War, when it was used to establish the position of artillery, air defense units and aircraft.

The system also has peaceful applications. The defense department has allowed civilians to use the satellites for several years. Using a technique known as “differential positioning,” surveyors are able to determine — to a fraction of an inch — the position of two GPS receivers tracking the same satellite signals.

Barry arranged to have all nine civilian GPS receivers in Maine available for the Epping Base Line measurement project. On Oct. 19, 1991, about 40 people gathered to check the accuracy of Bache’s 134-year-old measurements.

The group included members of the surveyors society, representatives of governmental agencies including the National Geodetic Survey, and students from the University of Maine department of surveying engineering.

In a few hours, the group repeated measurements that took weeks in 1857. They made observations from four points along the base line and nine other sites in eastern Maine.

The final calculations haven’t been made. Nelson says privately that Bache’s measurement of the 5.4-mile line could be accurate within a fraction of an inch.

“I’m constantly amazed at the technology that existed in the 1800s, and how it is still valid today,” said Nelson. “It gives you a good feeling.”

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