Articles written in Proceedings – Section A
Volume 24 Issue 1 July 1946 pp 176-181
Arguments are adduced to show that the doublet centred at 4152 Å occurring in the spectrum of all fluorescing diamonds arises from ‘forbidden’ transitions analogous to the forbidden3P-1S transitions in the spectrum of C I. On the basis of this analogy, fluorescence lines are also expected to occur at about 8816 Å and 7849 Å, analogous to the3P-1D and1D-1S transitions in C I. Of these, the former should also occur in absorption, while the latter should not occur in absorption and should be emitted only if the exciting radiation has a wavelength shorter than 4152 Å. A line has actually been found at 7930 Å, satisfying the latter conditions. The former line could not be recorded being outside the limit of sensitivity of the photographic plate.
Volume 24 Issue 1 July 1946 pp 182-186
Phosphorescence patterns in a dozen cleavage plates of diamond revealing the variations in intensity of phosphorescence in different portions of the same diamond have been successfully recorded by the method of contact photography. Comparison of these with the fluorescence patterns in the same diamond shows that the yellow phosphorescence emission corresponds to the blue fluorescence patterns, and that the yellow fluorescence patterns, if present, are not recorded in phosphorescence. Geometric patterns such as parallel bands, triangles, hexagons and spirals have been obtained in many cases.
Volume 24 Issue 1 July 1946 pp 187-192
Volume 24 Issue 1 July 1946 pp 193-197
Volume 25 Issue 3 March 1947 pp 256-259
When a plane-polarised beam of the intense λ 2537 radiation from a water-cooled, magnet-controlled mercury arc is sent along the optic axis of a perfectly clear and transparent sphere of quartz crystal free from inclusions, the track when photographed from a direction transverse to the beam exhibits striking fluctuations in intensity along its length. The effect, which is reproduced in the paper, is obviously connected with the rotation of the plane of polarisation of the polarised λ 2537 radiation as it traverses the crystal. The distance between one dark band to the next corresponds closely to a rotation of 180° of the plane of polarisation of the λ 2537 radiation. A similar effect was observed and photographed in smoky quartz by the present Lord Rayleigh in 1919 using the Tyndall scattering of visible light by the inclusions in the crystal. In the present case the effect is due to the diffusion of light arising from the atomic vibrations in the crystal lattice, and the clearness of the bands indicates that such scattering is strongly polarised.
Volume 26 Issue 2 August 1947 pp 110-113
Volume 27 Issue 4 April 1948 pp 316-320
The electronic line at λ 4156 present in the fluorescence spectrum of all diamonds sharpens and increases in peak intensity on cooling the diamond;
The phosphorescence of diamond at various temperatures has also been dealt with. At low temperatures the after-glow is weak and greenish-yellow in colour, while at 400° C., the glow is extremely intense and blue. The effect of quenching by red or green light on this bright and blue glow has been reported in this paper.
Volume 28 Issue 5 November 1948 pp 409-416
Volume 31 Issue 6 June 1950 pp 427-434
Volume 32 Issue 6 December 1950 pp 374-378
As in the case of quartz (Chandrasekharan, 1948), using the property of optical activity, the selection rules for Raman lines of sodium chlorate have been experimentally verified using λ 2537 excitation for two different orientations of the crystal. Its 15 Raman lines have been classified as follows into the various symmetry classes possible for a cubic crystal:— 70 (E), 83 (F), 103 (F), 123 (F), 131 (A), 179 (E), 482 (E), 487 (F), 627 (A+F), 933 (F), 936 (A), 959 (E), 966 (F), 984 (F), 1026 (−). The results agree with earlier ones of Couture and Mathieu (1948) except for the Raman line 131 cm.−1 which they classify as belonging to Class E.
The Brillouin components are well polarised and weaker than the symmetric Raman line 936 cm.−1
Volume 32 Issue 6 December 1950 pp 379-385
Volume 33 Issue 3 March 1951 pp 183-198
For the first time, the theory of Doppler shifts in thermal scattering of light in birefringent crystals is worked out and the magnitude of the shift Δ
In singly refracting crystals (
Volume 33 Issue 3 March 1951 pp 199-215
Sodium chlorate is the first crystal belonging to the tetrahedrite class (T) of the cubic system for which photoelastic constants have been measured. Since the crystal exhibits optical activity and no birefringence in the absence of stress, special techniques have to be adopted for measuring the birefringence introduced by stress. This has been done by the use of a petrological microscope in conjunction with the stressing apparatus and measuring the ellipticity and other characteristics of the light transmitted by the crystal. A particularly simple method is to use the “elliptic analyser”. Since the crystal does not possess four-fold axes, the relative orientation of the X- Y- and Z-axes was determined by means of X-rays. From observations on crystals compressed along ,  and  directions,