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.

Ships entering the harbor are not directly visible from the wharfs, which created problems for merchants trying to prepare for the arrival of cargoes.

This problem was solved in 1807 when Captain Lemuel Moody[1] organized the construction of an observatory on Portland's Munjoy Hill, visible from both the open ocean and the wharfs.

The 86-foot (26 m) tall observatory (7 stories) is octagonal (to lessen wind pressure on each side) and lighthouse-shaped, with a fieldstone base of heavy loose rocks, and stands 222 feet (68 m) above sea level.

The observatory's 'lantern' (cupola) included a P & J Dollond Achromatic Refracting Telescope, which could identify ships 30 miles (48 km) to sea.

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.