Studies in the photometry of lights of different colours / by Herbert E. Ives. : spectral luminosity curves obtained by the equality of brightness photometer and the flicker photometer under similar conditions.

  • Ives, Herbert Eugene, 1882-1953.
Date:
[1912]
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Licence: In copyright

Credit: Studies in the photometry of lights of different colours / by Herbert E. Ives. : spectral luminosity curves obtained by the equality of brightness photometer and the flicker photometer under similar conditions. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    the middle. He plots critical frequencies for constant slit- width, instead of slit-widths or reciprocal slit-widths for constant frequency as is here done. It is in this difference Fig. 2. «oc «30 4<oO tao ,reo sso seo t>so 6va 6?o 7oo 730 7*0 Critical Frequencies of the spectral colours at high, medium, and low- intensities, showing- relatively greater change for red (R). After Haycraft. of procedure that we find the explanation of the difference between Hay craft's results and those of the present writer. An examination of Haycraft's curves indicates that in all cases the end portions of the spectrum are at illuminations calling for lower critical speeds than the low curve obtained by the writer. Curve C, fig. 1, corresponds to 18 cycles per second, while Haycraft's speeds vary from 19 to about 4 cycles per second. After noting this fact an additional critical frequency curve (Curve D) was determined for an illumination less than a tenth that of Curve 0. This shows, with respect to the one at 5 I. XL, a pronounced Purkinje shift, in qualitative agreement with Haycraft. Apparently, therefore, the changes which accompany decreasing illumination are first in one direction and then in the other. In searching for some other phenomena of critical frequency with which this might be coordinated, it occurred to the writer that the regions of the Purkinje and the reversed Purkinje effect might be connected with the