19th century in science Carnot captured some of the ideas of thermodynamics in his discussion of the efficiency of an idealized engine. Sadi Carnot's work provided a basis for the formulation of the first law of thermodynamics—a restatement of the law of conservation of energy—which was stated around 1850 by William Thomson, later known as Lord Kelvin, and Rudolf Clausius. Lord Kelvin, who had extended the concept of absolute zero from gases to all substances in 1848, drew upon the engineering theory of Lazare Carnot, Sadi Carnot, and Émile Clapeyron–as well as the experimentation of James Prescott Joule on the interchangeability of mechanical, chemical,
Christianity in the 19th century regulation of working conditions. "Rerum novarum" argued for the establishment of a living wage and the right of workers to form trade unions. Popes have always highlighted the inner link between the Virgin Mary as Mother of God and the full acceptance of Jesus Christ as Son of God. Since the 19th century, they were highly important for the development of mariology to explain the veneration of Mary through their decisions not only in the area of Marian beliefs (Mariology) but also Marian practices and devotions. Before the 19th century, popes promulgated Marian veneration by authorizing new Marian feast days,