The conservation of energy, theories of absorption and resonating molecules, 1851-1854: G. G. Stokes, A. J. Ångström and W. Thomson

Abstract

That heat and light were varieties of the same phenomenon, i.e. vibrations in an all pervading aether, came to be widely accepted in the 1840s and ’50s (1). This was also the period when the principle of the conservation of energy was developed and applied. While a great deal has been written on the development of the principle (2), there has been comparatively little discussion on the manner in which the principle was applied. It was quickly realized that the principle had immediate applications to the study of nature in all her forms as Hermann Helm holtz pointed out in his Ueber die Erhaltung der Kraft (3). My object in this paper is to trace the application of the principle to optical phenomena and in particular to that most contentious of phenomena— the absorption of light (4). The two scientists who considered this problem were George Gabriel Stokes (5), Lucasian Professor of Mathematics at Cam ­ bridge, and Anders Jonas Angstrom (6), assistant Professor of Astronomy at Uppsala. In establishing his version of the undulatory theory of light, Augustin Fresnel (7) had considered only the mathematical behaviour of light waves. He had not dealt in any depth with the physical meaning of waves propagated in the aether. Because the double refraction and polarization of light required waves to be transversely propagated, he maintained that the aether needed to do this must necessarily exist (8). Fresnel in developing his theory had restricted his study to explaining either phenomena which were not affected by the material nature of the body which caused them (e.g. diffraction), or phenomena which were dependent on a special structure of matter (e.g. double refraction and polarization).