Samuel Lytler Metcalfe (1798–1856) was an American chemist and physician who wrote a voluminous work, Caloric Its Mechanical Chemical and Vital Agencies in the Phenomena of Nature (2 vols., London, 1843); attempting to account for all natural phenomena in terms of caloric. The book came out at the time when the concept of caloric was being gradually discarded and the law of conservation of energy was about to appear. Metcalfe was convinced that caloric would be the key to unlock the secrets of nature; in order to develop the practical implications of his views he made research trips twice to England (1831 and 1835–45), and there he completed Caloric.