"The first formulation of (part of) mechanics by means of a variational principle... is due to Maupertuis in 1746 in a paper called "Les lois du mouvement et du repos déduites d'un principe métaphysique" (Laws of motion and rest deduced from a metaphysical principle). Maupertuis had first introduced the principle of least action in optics in 1744. ...Through experimentation, he found that this quantity depends on mass, velocity, and distance. He called the product of the three factors "action" and accordingly expressed a "principle of the least quantity of action"..."