The Laplace operator is named after the French mathematician Pierre-Simon de Laplace (1749–1827), who first applied the operator to the study of celestial mechanics. In this case, the operator gives a constant multiple of the mass density—when it is applied to a given gravitational potential. Solutions of the equation ∆"f" = 0, now called Laplace's equation, are the so-called harmonic functions, and represent the possible gravitational fields in free space.