Meridian Stones Mystery Is Solved
Many island visitors wonder about the meaning of the two stone obelisks downtown: one on upper Main Street and one on Fair Street. The purpose of the two stone monuments has long been one of Nantucket’s great historical mysteries. Thanks to the work of a group of researchers inspired and led by the Maria Mitchell Association, the mystery has been solved. And on October 2 at 5 pm, a plaque will be unveiled at the Pacific National Bank that marks the work of William Mitchell, who was responsible for the stones, and Maria Mitchell, his daughter and noted astronomer.
It was known that the stones had been erected by the Town in 1840, based on a proposal of William Mitchell (1791-1868), the most prominent astronomer and surveyor on Nantucket at that time and the father of the first American woman professional astronomer, Maria Mitchell (1818-1889). However, the exact reason these stones were cut and placed was unknown until recently.
In 2002, a group of enthusiasts led by the Maria Mitchell Association (MMA), set out to solve the mystery. The project took several years. Two MMA summer students participated in the project and one of them, Lucy Amory, a history major from Vassar College, finally found archival materials that clarified the purpose of the stones.
The stones were erected by Mitchell, using precise astronomical methods, to represent the true geographic meridian (north-south line). They were used for monitoring the variations of the angle between the true North and the magnetic North (the so called “magnetic declination”). The direction to the magnetic North was the working reference direction for the surveyors of that epoch who used a compass to measure bearings. An accurate correction for the magnetic declination was necessary to present the results of the survey on a geographic map, where the reference direction is true North (not magnetic).
The investigation showed further that the Mitchell Meridian Line was one of the first of this kind in the country. Mitchell’s stones preceded the mandatory installation of similar constructs elsewhere in Massachusetts and other states by three decades. The Massachusetts General Court passed a resolution in 1870 that required the installation of “true meridian lines” in every county.
The memorial plaque being presented on October 2 is installed on the wall of the Pacific Bank, next to the Northern Meridian Stone. It celebrates the memory of two distinguished residents of our island – William and Maria Mitchell who brought to Nantucket one of the important flavors of its fame – to be an “Astronomical Island.”
The Maria Mitchell Association invites the public to join them in toasting Mitchell’s trailblazing work. At 5 pm a brief history of the stones will be given, the plaque will be unveiled, and light refreshments served. The toast will take place in the Land Bank Fair Street Park, on the corner of Main and Fair sts across from the Bank.
