„I must now explain what I mean by the quantity of action. A certain action is necessary for the carrying of a body from one point to another: this action depends on the velocity which the body has and the space which it describes; but it is neither the velocity nor the space taken separately. The quantity of action varies directly as the velocity and the length of path described; it is proportional to the sum of the spaces, each being multiplied by the velocity with which the body describes it. It is this quantity of action which is here the true expense (dépense) of nature, and which she economizes as much as possible in the motion of light.“
— Pierre Louis Maupertuis
Histoire de l'Academie (1744) p. 423; Les Oeuvres De Mr. De Maupertuis (1752) vol. iv p. 17; as quoted by Philip Edward Bertrand Jourdain, The Principle of Least Action https://books.google.com/books?id=y3UVAQAAIAAJ (1913) p. 5.