The principle was also championed by some chemists such as William Hyde Wollaston. The French mathematician Émilie du Châtelet, who had a sound grasp of Newtonian mechanics, developed Leibniz's concept and, combining it with the observations of Willem 's Gravesande, showed that vis viva was dependent on the square of the velocities. Members of the academic establishment such as John Playfair were quick to point out that kinetic energy is clearly not conserved. This is obvious to a modern analysis based on the second law of thermodynamics, but in the 18th and 19th centuries, the fate of the lost energy was still unknown. Gradually it came to be suspected that the heat inevitably generated by motion was another form of vis viva. In 1783, Antoine Lavoisier and Pierre-Simon Laplace reviewed the two competing theories of vis viva and caloric theory. Count Rumford's 1798 observations of heat generation during the boring of cannons added more weight to the view that mechanical motion could be converted into heat. Vis viva began to be known as energy after Thomas Young first used the term in 1807. The recalibration of vis viva to include the coefficient of a half, namely: was largely the result of the work of Gaspard-Gustave Coriolis and Jean-Victor Poncelet over the period 1819–1839, although the present-day definition can occasionally be found earlier (e.g., in Daniel Bernoulli's texts). The former called it the quantité de travail (quantity of work) and the latter, travail mécanique (mechanical work) and both championed its use in engineering calculation. See also Conservation of energy: Historical development Élan vital Kinetic energy Orthogenesis Potentiality and actuality Vis-viva equation Notes References George E. Smith, "The Vis Viva Dispute: A Controversy at the Dawn of Dynamics", Physics Today 59 (October 2006) Issue 10 pp 31–36. (see also erratum) Natural philosophy Obsolete theories in physics Mechanics Thermodynamics Gottfried Wilhelm Leibniz History of thermodynamics