Joule was the first to measure with accuracy the mechanical equivalent of heat (in 1856). Since 1860, the mechanical theory of heat has been considered as one of the greatest conquests af science in the nineteenth century. Its applications both in science and industry are countless.
Mendéléeff, Dmitri (1834–1907), a remarkable Russian chemist, best known for his discovery of the "Periodic Law of Elements." It is known that all the bodies which we find on the earth’s surface, whether living or dead matter, are composed of some eighty or ninety different bodies, which cannot be decomposed, and therefore are named elements. These enter among themselves into an infinite number of combinations. The elements, Mendéléeff discovered, if we write them down in the order of the increasing complexity of their molecules, can be disposed in a table containing eight vertical columns and twelve horizontal lines. If such a table is made, it appears that all the elements placed in each column will have some chemical properties in common; so also all the elements inscribed in each horizontal row—the energy of the chemical properties increasing in each row as you go from Column 1 to Column 8. This suggests the idea (1) that the molecule of each element is probably a complex system of still smaller molecules (or rather atoms) in continual movement round each other—like the planets Jupiter or Saturn, with their several moons; and (2) that in the structure of these systems there is a certain periodicity, i.e., a repetition of some scheme of structure. This discovery has immensely helped the development of chemistry. His conception of the cosmical ether as matter, the atoms of which are in vibrations so rapid that they cannot be fixed and kept in more or less permanent chemical combinations, though yet less known, is equally important.
Mill, John Stuart (1806–1873), famous English economist and philosopher. One of the most eminent representatives of "empiricism," i.e., of research based on observation. In his "System of Logic" he has admirably developed the theory of the inductive method. Author of "Principles of Political Economy," "Essay on Liberty," and "Representative Government."
Moleschott, Jacob (1822–1893), a materialist physiologist of Dutch origin. Wrote, in German, many works to popularise materialist philosophy; one of them, "The Cycle of Life" ("Kreislauf des Lebens"), had a wide renown.
Owen, Robert (1771–1858), with Fourier and Saint-Simon one of the three great founders of modern Socialism—especially of associated Trade Unionism and federated Co-operation. Exercised a deep influence upon his contemporaries in England, both among the working men and the intellectuals, inspiring both with higher ideals of equality, freedom, and justice. The severe prosecutions which were begun against his followers in 1831, after he had started the great Union of all trades—which was