138 Congress Street
Portland, Cumberland County, Maine, 04101
The Portland Observatory is a historic maritime signal tower. Built in 1807, it is the only known surviving tower of its type in the United States.
Using both a telescope and signal flags, two-way communication between ship and shore was possible several hours before an incoming vessel reached the docks.
The 86-foot (26 m) tall observatory (7 stories) is octagonal (to lessen wind pressure on each side) and lighthouse-shaped, with a field stone base of heavy loose rocks, and stands 222 feet (68 m) above sea level. There is no basement but the rock ballast in the bottom floor and octagonal design have kept the structure steady during storms.
The observatory's 'lantern' (cupola) included a P & J Dolland Achromatic Refracting Telescope, which could identify ships 30 miles (48 km) to sea. That telescope disappeared from the observatory in 1939.
Tower operations were paid with annual fees collected from shipping merchants, who purchased the right to have their flags stored in the building and hoisted up its flagstaffs when their ships were sighted. A telephone was eventually installed, extending the tower's function until 1923, when the reliability of engine powered vessels and communication by radio made it obsolete.
Greater Portland Landmarks, a non-profit organization, maintains the building. Guided tours with discussion about the history of the building and the neighborhood are provided by volunteer docents from Memorial Day to Columbus Day for a small fee. On very clear days the view from the cupola's balcony extends from the seaward horizon as far inland as Mount Washington.
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