His many achievements include work on planetary orbits , measuring the mean density of the Earth , a method of solution of two-dimensional problems in solid mechanics and , in his role as Astronomer Royal , establishing Greenwich as the location of the prime meridian .
His many achievements include work on planetary orbits , measuring the mean density of the Earth , a method of solution of two-dimensional problems in solid mechanics and , in his role as Astronomer Royal , establishing Greenwich at the location of the prime meridian .