Photo-chemistry / by S.E. Sheppard.

  • Samuel Edward Sheppard
Date:
1914
Catalogue details

Licence: In copyright

Credit: Photo-chemistry / by S.E. Sheppard. Source: Wellcome Collection.

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    a partial polarization equal to that in a plane perpendicular to its own produced by the dispersion prism. Where high extinctions have to be measured, a convenient adjunct is a subsidiary extinction, which is best made of a photographic plate developed with ferrous oxalate and used, after careful measurement of its light-absorbing power, as a cap on the polarizing Nicol. Since I = I0 cos2 0, the extinction-coefficient (vide p. 136) e = — 2 log cos 0. Other polarizing spectrophotometers have been designed by Glazebrook,1 Crova,2 A. Wild,3 A. Konig,4 and J. Konigs- berger.5 The photometers of Wild and Kbnigsberger utilize the vanishing of interference fringes as a criterion that the two fields are equal. Two ray-bundles proceeding from a divided collimator-slit are polarized by a Senarmont or Thomson prism,3 and then pass through a rhomb of Iceland spar. There issues from this a single ray-bundle, consisting of the ordinarily refracted ray from one-half of the slit, and the extraordinarily refracted rays from the other. This, after passing the disper- sion prism, traverses a Savart7 interference plate, and, finally, another polarizing prism. Interfering fringes in the Savart plate vanish when the united bundle contains equal quantities of light polarized at right angles to each other, i.e. when I = I0. P tan2 a, where a is the angle which the plane of polariza- tion of the first polarizing prism makes with the principal section of the Iceland-spar rhomb, and P is an empirically determined constant. Konigsberger’s instrument was a micro- photometer, based on the same principle, for determining the absorption relations of crystals.3 As before remarked, the 1 Proc. Cambridge Philos. Soc., 4, 304. - Ann. de Chitn. et Phys., [5] 29, 556 (1883). 3 Wied. Ann., 20, 452 (1883). 4 Ibid., 53, 785 (1894). 5 Zeit sc hr. f. Inst. Kunde, 21, 129 (1901) ; 22, 129 (1902). 0 For different forms of polarizing prisms, see T. Preston, Theory of Light, 2nd edit., pp. 312-315, 449-466. ’ See Preston’s Light, p. 402. 8 T. Konigsberger, “ Dependence of Absorption of Solid Bodies on the Temperature,” Ann. d. Phys., [4] 309, 796 (1901).
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