John William Strutt, third baron Rayleigh, O.M., F.R.S., sometime president of the Royal society and chancellor of the University of Cambridge / by his son Robert John Strutt, fourth baron Rayleigh.

  • Rayleigh, Robert John Strutt, Baron, 1875-1947.
Date:
1924
Catalogue details

Licence: In copyright

Credit: John William Strutt, third baron Rayleigh, O.M., F.R.S., sometime president of the Royal society and chancellor of the University of Cambridge / by his son Robert John Strutt, fourth baron Rayleigh. Source: Wellcome Collection.

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    and at the same time the closely related question of why it shows the peculiar phenomena of polarization which had been examined early in the century by Arago, Biot, and Brewster. Needless to say, these questions had been considered before. Some earlier writers, notably Clausius, had supposed the light to be reflected from thin plates, and the colour to be the blue of the first order in Newton’s scale. Clausius assumed the existence of bubbles floating in the upper atmosphere of the appropriate thickness to give this effect. But this theory, besides requiring a rather forced ad hoc supposition, indicates a blue colour less rich than that which actually prevails. A better theory was advocated by Tyndall, whose beautiful experiments showed that the blue sky could be imitated by passing the beam of the electric arc through certain organic vapours. These gave clouds of extremely firm particles which scattered laterally light of a blue colour. A more familiar though less perfect illustration is found in the blue light scattered from tobacco smoke. The light scattered at right- angles in this way is almost completely polarized, and in this respect also corresponds approximately with the light emitted from the sky in a direction at right-angles to the sun. Tyndall considered it very strange that, as he expressed it, the polarizing angle for matter in this condition should be 45°, apparently considering that when light was diverted through a right-angle by a cloud of particles the case had some analogy with reflection from a glass surface placed at 45°. Strutt pointed out that according to the principles of the wave theory such a comparison was wholly illusory. He then went on to consider the question from the standpoint of the theory which assimilates the vibrations of light to those of an elastic solid. This theory in its literal form is of course obsolete, but for many purposes it remains even now a perfectly valid instrument of research. Its limitations were recognized clearly at the time, as the following quotation shows; “ The fact that the theory of elastic solids led Green to