 The Marburg philosophers wrote several works that engaged in a detailed way with the natural science, especially physics, of their day. In his Forward and Introduction to the sixth edition of Lange’s History of Materialism, first published in 1898, Cohen gives a philosophical interpretation of work on electromagnetism since Faraday, and defends Hertz’s Principles of Mechanics (Hertz 1894). In two works both published in 1910 (Natorp 1910: Ch.7; Cassirer 1910: Ch.4) Natorp and Cassirer discuss foundational issues in physics: the principles of mechanics and thermodynamics; the nature of mass, energy, space, and time; atomism and its critics. (Cassirer also addresses foundational issues in chemistry: 1910: Ch.4, section 8). The culmination of this work is Cassirer’s Einstein’s Theory of Relativity, published in 1921.