At night, in the fog, or in a storm, lighthouses act as guideposts for ships. Lighthouses warn sailors so they don't hit land or other obstructions in the water. They are built on harbors, islands, and beaches. Many years ago, people set fires at the edge of the water to warn boats of dangerous rocks and shores. The Egyptians are the first people known to have built lighthouses to guide ships. Lighthouses were also constructed by the Phoenicians, Greeks, and the Romans. The first lighthouse in England was the Eddystone Rock Lighthouse built on a steep rock in 1698. The first lighthouse in America, lit in 1716, was the Boston Lighthouse on Brewser Island in Boston Harbor.
Early lighthouses used wick lamps as a source of light; the light beam could only travel a few miles. In 1822 the first modern lighthouse lens was invented by a Frenchman named Augustin Fesnel. Fresnel discovered how to increase light by using prisms. In 1841, the Fresnel lens was installed for the first time in a lighthouse.
Lighthouses were operated by keepers who had to make sure that the lights were burning and fog bells were ringing at night, in fog, storms, or any condition that limited visual acuity. The lighthouse keeper often rang bells and even shot cannons as a warning to ships. A keeper's house was either built into a lighthouse or constructed separately close to the lighthouse. Today most lighthouses have lights that run automatically using electricity.
Lighthouses have played an important role in the history of the Hudson River. The Stony Point Lighthouse was built as early as 1826. Fourteen lighthouses were built along the Hudson River, including two at the Rondout Creek in Kingston and a post light with a fog bell at Danskammer Point. There were also numerous other post lights up and down the river. Today only seven lighthouses remain.