Light Scattering

Abstract

In the first nine sections of his fourth lecture on light, John Tyndall explained how crystals rotate the plane of polarization of light passing through them: it is a consequence of the different refractive indices along different crystal axes. Thus, Tyndall identifies structural asymmetry—and its effect on the transverse vibrations of interatomic ether—as the cause of birefringence in crystals. In the final sections of his fourth lecture on light, included in the present chapter, we will see how particles suspended in a transparent medium also affect light propagation. But before moving on to this fascinating topic, Tyndall pauses to emphasizes how the undulatory theory of light provides a powerful organizing principle for understanding all of the surprising and beautiful phenomena thus far observed. Does Tyndall believe that the undulatory theory of light is true, or merely useful? How would you describe his philosophy of science?

How, if the air be blue, can the light of sunrise and sunset, which travels through vast distances of air, be yellow, orange, or even red?

—John Tyndall