In order to make it easier to describe elements and molecules, chemical formulas are used. For example, H represents one atom of hydrogen and O represents one atom of oxygen. If we want to represent two atoms of hydrogen, instead of writing H H, we write H2.
This car is named for Promontory Summit, Utah, just north of Great Salt Lake and the site selected for the joining of the Union Pacific and Central Pacific Railroads. Completion of the railroadâthe greatest engineering feat of the 19th centuryâculminated in a celebration there on May 10, 1869. Promontory Point, often erroneously referred to as the location for the ceremony, juts out into the lake itself. It was the location of a saltworks for many years.
Located on rocky coasts, towering cliffs, and on islands, lighthouses serve as beacons, guiding ships safely into harbor at night or during a storm. Coastal lighthouses were first constructed in the 17th century to warn mariners of dangerous rocks, reefs, and currents, according to the Lighthouse Preservation Society. By 1900, nearly 1,000 lighthouses had been built in the US; and today, there are nearly 50,000 lighthouses in existence.