The Lorenz-Lorentz Formula: Origin and Early History

Keywords: L. Lorenz, H. A. Lorentz, optical refraction, Clausius-Mossotti formula, molecular refractivity


Among the many eponymous formulae and laws met in textbooks in physics and chemistry, the Lorenz-Lorentz formula merits attention from a historical point of view. The somewhat curious name of this formula, which relates the refractive index of a substance to its density, reflects its dual origin in two areas of nineteenth-century physics, namely optics and electromagnetism. Although usually dated to 1880, the formula was first established in 1869 by L. V. Lorenz (optics) and subsequently in 1878 by H. A. Lorentz (electromagnetism). Apart from discussing the origin and priority of the Lorenz-Lorentz formula the paper outlines its early use in molecular physics and physical chemistry. During the late nineteenth century studies of molecular refractivity based on the formula proved important in a number of ways. For example, they led to estimates of the size of molecules and provided information about the structure of chemical compounds.

Author Biography

Helge Kragh , Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, Copenhagen, Denmark

Helge Kragh is Emeritus Professor at the Niels Bohr Institute in Copenhagen and a former Professor of History of Science at the universities of Oslo, Norway, and Aarhus, Denmark. During 2008-2010 he served as President of the European Society for the History of Science. He works primarily in the history of post-1850 physical sciences, including chemistry, astronomy and cosmology. In 2015 he co-edited, with M. Kaji and G. Palló, Early Responses to the Periodic System (Oxford University Press).

How to Cite
Kragh , H. (2018). The Lorenz-Lorentz Formula: Origin and Early History. Substantia, 2(2), 7-18.
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