On a new case of the interference of light / by the Rev. Baden Powell.

  • Powell, Baden, 1796-1860.
Date:
1848
Catalogue details

Licence: Public Domain Mark

Credit: On a new case of the interference of light / by the Rev. Baden Powell. Source: Wellcome Collection.

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    XV. On a new Case of the Interference of Light. By the Rev. Baden Powell, M.A.^ F.R.S., F.R.A.S., F.G.S.^ Savilian Professor of Geometry in the University of Oxford. Received April 6,—Read May 18, 1848. (1.) In the state of advance at which the theory of light has now arrived, a single case of interference directly explicable by the ordinary principles of undulations, even though oceurring under new conditions, could hardly be deemed of sufficient iinportanee to form the subject of a separate communication to the Royal So- ciety. But in the present instance though the ease presented, in its more gewera/features, is easily aecounted for on the acknowledged doetrine of interference and retardation, yet it offers many particulars in its details, in reference to which such explanation is, at least, not equally obvious: while some points require for their elucidation investi- gations of a more extended eharacter. Again, it is found to be a ease which by no means stands isolated, but offers ana- logies with other elasses of phenomena whieh have exeited considerable interest and discussion, especially with regard to what has been termed, perhaps improperly, a “ polarity” in the prismatic rays,’—a new instanee of whieh is here exhibited. In these respects, then, I trust the subject may not appear unworthy of the notice of the Royal Society. Having arrived at the primary results in July 1847, I communieated them to my friend Mr. G. G. Stokes of Pembroke College, Cambridge, who has gone extensively into the whole theory of these and other allied cases, and has afforded me much valu- able aid in the investigation. In the present paper I propose only to describe my own experiments, with the general application of the undulatory theory to the expla- nation of them, supported by some numerical comparisons. (2.) The main experiment is as follows :—in a hollow glass prism, or rather trough, containing some highly refractive and dispersive liquid, such as oil of sassafras, anise, or cassia, a plate of glass is inserted with its lower edge parallel to the edge of the prism, and so that its plane nearly bisects the angle of the prism, while it extends only through the upper half of the liquid, leaving the lower, or thinner part, clear (see fig. 1). Light being admitted through a narrow horizontal slit in the usual manner, the spectrum thus formed is seen crossed hy a number of dark bands parallel to the slit or edge of the prism. 2 F 2