The Washington meridians are four meridians that were used as prime meridians in the United States and pass through Washington, D.C. The four which have been specified are: 1. * through the Capitol 2. * through the White House 3. * through the old Naval Observatory 4. * through the new Naval Observatory. Their longitudes may be reported in three ways: NAD83 longitude of the Capitol is about 1.1 arc seconds less than its NAD27 longitude; astronomic longitude there is about 4 arc seconds less than NAD83.