Radiation Pressure in a Refracting Medium

Abstract

THE measurements of electromagnetic radiation pressure in a vacuum by Lebedew¹, and by Nichols and Hull², are among the classic experiments of physics. All the theories that predict this pressure also predict that it should increase in a refracting medium. On the early corpuscular theory, the corpuscles are accelerated as they pass into a medium of higher refractive index; on the wave theory, the energy density increases as the waves slow down in the denser medium; on quantum theory the corresponding momentum of each photon increases, since it is equal to h/λ (where h is Planck's constant and λ is wave-length). An experiment to detect the increase of radiation pressure in an optically denser medium is not a crucial one, since the expected increase on each theory is the same; nevertheless, it is desirable that the increase should be observed.