The English physicist James Prescott Joule (1818–1889) was the son of a wealthy brewer. Although many of his discoveries were not widely accepted for many years, by the end of his career he had made significant contributions to the understanding of how different forms of energy (such as electrical, kinetic, and heat energy) are related. Today, along with the German physician and scientist Julius Robert von Mayer (1814–1878), Joule is credited with figuring out the mathematical conversion factor between heat and kinetic energy. The physical unit for kinetic energy is called the joule (J) in his honor (one joule is equal to 0.239 calories).