<Table> <Tr> <Td> </Td> <Td> This section needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (November 2015) (Learn how and when to remove this template message) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This section needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (November 2015) (Learn how and when to remove this template message) </Td> </Tr> <P> Ancient philosophers as far back as Thales of Miletus c. 550 BCE had inklings of the conservation of some underlying substance of which everything is made . However, there is no particular reason to identify this with what we know today as "mass - energy" (for example, Thales thought it was water). Empedocles (490--430 BCE) wrote that in his universal system, composed of four roots (earth, air, water, fire), "nothing comes to be or perishes"; instead, these elements suffer continual rearrangement . </P> <P> In 1605, Simon Stevinus was able to solve a number of problems in statics based on the principle that perpetual motion was impossible . </P>

Who discovered the law of conservation of energy