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]

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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$much less for small fields. That is, by using high illuminations and small fields the differences between the methods are less than for low illuminations and large fields. At once there opens the possibility that by proper choice of illumination and field-size the two methods may agree. Should this be the case, it would be a strong argument for choosing that illumi- nation and field-size as the standard one for making colour comparisons. The possibility thus indicated is sufficient for undertaking a complete comparison of the methods. Apparatus and Procedure. The method of attacking the problem was to determine by the two methods and under various conditions the lumi- nosity curves of a spectrum of known energy distribution. The apparatus used is similar in some respects to that of Tufts, and is shown in fig. 1. A Hilger constant-deviation Fig. 1.—Arrangement of Apparatus. 1. Observing slit. 6. White sector-disk. 10. Light source. 2. Prism table. 7. Photometer bench. 11. Photometer bench. 3. Collimator slit. 8. Standard lamp. 12. Diaphragm. 4. Divided drum. 9. Diffusing glass. 13. Diaphragms used. 5. Wave-length drum. wave-length spectrometer forms a spectrum of the light source upon an eye-slit (1) of dimensions \ by 2 mm. The eye placed at this slit observes the prism face (2) illuminated Phil. Mag. S. 6. Vol. 24. No 139. July 1912. M$