Even a sailor's reputed eagle's vision did not reach far enough for safety. Whether searching for a
coast line or spotting a privateer's top sails over the horizon, the telescope was one of the
essentials of seafaring life. Instrument makers specializing in the astronomical telescopes as
invented by Galileo soon introduced the naval spyglasses. Binoculars surfaced by the middle of the
18th century, but the long tube telescopes continued to be used well into the 20th century.