Frederick Soddy (1877-1956), an English chemist who was awarded the 1921 Nobel Prize in Chemistry for his discovery of isotopes. Soddy is also known for applying the laws of energy to social and economic theory. His formulation of the concept of isotopes in 1913 stated that certain elements exist in two or more forms that have different atomic weights but are indistinguishable chemically. He also postulated his "Displacement Law", namely that emission of an alpha particle from an element causes that element to move back two places in the periodic table. In Wealth, Virtual Wealth and Debt (1926), Soddy turned his attention to the role of energy in economic systems. He criticized the focus on monetary flows in economics, arguing that “real” wealth was derived from the use of energy to transform materials into physical goods and services. Soddy’s writings were largely ignored in his time, but would later be applied to the development of biophysical and ecological economics in the late 20th century.