The time of perception as a measure of differences in sensations / by Vivian Allen Charles Henmon.

  • Henmon, Vivian Allen Charles (V. A. C.), 1877-
Date:
1906
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Licence: In copyright

Credit: The time of perception as a measure of differences in sensations / by Vivian Allen Charles Henmon. Source: Wellcome Collection.

Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.

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    Mandelstamm.,^ using the Helmholtz ophthalmometer, determined the just perceptible differences in color-tone at Fraunhofer’s lines and four undefined intermediate points. The method was to observe the solar spectrum through the ophthalmometer plates so placed as to give two adjacent colored fields. By rotation of the plates, alteration of the color-tone could be brought about. A slit in the ocular gave approximately monochromatic light. The maximum sensitivity was found in the yellow region (D), a second maximum in blue (F), and a third in blue-green (E-F). The sensitivity was considerably less for indigo (G), green (E), violet (G-H), and least of all for red (C). Dobrowolsky^ used the same apparatus as Mandelstamm with some alterations. In the carrying out of the experiments greater care was exercised to exclude differences in brightness. The method was as before to determine just noticeable differences. The results agreed with those obtained by Mandelstamm, though a much greater sensitive- ness was shown. The results are indicated by the following figures taken from Aubert’s Grundziige der Physiologischen Optik.^ B C C-D D D-E E E-F G G-H 1/115 1/167 1/331 i/772 1/246 1/340 1/740 1/272 1/146 B. 0. Peirce^ used a large spectroscope, into the collimator of which was inserted a sheet of vulcanite dividing the tube into an upper and a lower half. The slit in the upper part through which the light entered was movable to the right or to the left. The apparatus was further adjusted so that when the movable collimator slit was dis- placed, the color of the observer’s lower slit was changed without a change of position in the field. The spectrum was produced by a light from an Argand burner falling upon a Rutherford diffraction grating. The object of the experiment was to determine the smallest dis- placement ‘that could be infallibly detected and named in direction by the observer.’ The amount of the displacement was found to vary with different colors and with different observers. The largest dis- placement necessary for any observer was byp and the smallest .byy. The greatest sensitivity was found at a point near D, varying with the observers, ‘being in some cases more orange and in others more yellow.’' The second maximum was foimd at F. Between B and F there was a decrease. A third slight increase was found at Li. Dobrowolsky had found a similar increase at B, but later discovered that this was due to alteration in brightness. ' E. Mandelstamm, Griifes Archiv f. Ophth., 13, 2: 399 ff., 1867. ^ W. Dobrowolsky, Grafts Archivf. Ophth., 18; 102 ff., 1867. * H. Aubert, Grundziige der physiologischen Optik, Leipzig, p. 530, 1876. ‘ B. O. Peirce, Am. Jour. Sci., 3rd Series, 26: 299-302, 1883.