Material concerned with optical and visual phenomena produced by rotating discs- No links match your filters. Clear Filters
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Related toK. Marbe, 'Neue Versuche über intermittirende Gesichtsreize', Philosophische Studien 13 (1898), pp. 106-115.
Description:Describes experiments in which subjects are exposed to two successive light stimuli. Uses photographic technique developed previously to produce range of around 30 homogenous grey prints, ranging from almost black to almost white. Measures shades using rate of rotation of a white and grey disc. Goes on to compare this measured comparison of shades with the subjective experience of them, finding that the difference between the subjective and objective estimation of shades is subject to a law of relation.
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Related toO.F.F. Grünbaum, 'On Intermittent Stimulation of the Retina (Part I)', Journal of Physiology 21 (4-5) (1897), pp. 396-402.
Description:'The method adopted consisted in determininig at what frequency of alternation and at what luminosities fusion (disappearance of 'molecular' movement) occurred, when the ratio of the breadth of sector to the diameter of aperture varied from 1 to 20.
A series of discs were used from which a variable number of sectors had been cut 2-60, leaving an equal number of equiangular sectors: these were rotated by a motor, the speed of rotation being adjusted by altering the resistance in the motor circuit, and when necessary by varying the number of accumulators used to supply the current.
The discs were painted black on both surfaces, and were prevented from oscillating when revolving at high speeds by two pulleys. The speed of rotation was observed on a Napier's "show speed" indicator, which was found to be correct to 1 0/0 when standardised by the counter. The source of illumination was usually a 16 candle power electric lamp, one side of which was frosted and used as the screen; the lamp was usually run at 135 volts instead of 100, and thereby a much whiter light was produced than under ordinary conditions.' (397)
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Related toW. McDougall, 'Some New Observations in Support of Thomas Young's Theory of Light and Colour-Vision', Mind 10 (1) (1901), pp. 52-97, 210-245 and 347-382.
Description:'I have now shown that all the phenomena of contrast and induction of S [black] and W[hite] are to be explained without the hypothesis of a special S-exciting process in the retina. So far as I know the only remaining reason for retaining the hypothesis is the assertion that mixing S with a colour diminishes its saturation just as does mixing W with it. This statement rests upon observations of the kind that is described by [G.E.] Müller [note: 'Zeitschrift f. P. d. Sinnesorgane, Bd. xiv. p. 135.' (94)] in the paper before referred to.
He prepares two composite discs of which each has a middle zone made up of 40° of R[ed] and 320° of black cloth; in one which I will call A the rest of the disc is also of black cloth, and in the other B it is of W. If these two discs be rotated side by side on the colour wheel and fixated in turn the R of the ring on A appears more saturated than the R of the ring on B. How, asks Muller, can this be explained by those who do not accept the S-process hypothesis ?
In order to obtain light on this question, I made the following observation :—
Observation XXIV.— I made up two discs as follows : Disc A of black cloth with one section of W of about 90 ° — this on rotation appears of a light grey; and disc B of W paper with a ring of W and S in such proportion that oh rotation it appeared of the same brightness as disc A in spite of the
contrast darkening effect of the W ground. This required about 120° of W. Then to each nng I added 30° of R. On rotation the R of the ring on A was more saturated than that of the ring on B, and the difference was just about the same in degree as in the case of the two discs of Müller's experiment. I repeated this, varying the brightness of the grey used and also the amount' of R added, and the result was always the same, thus: e.g., with 20° of R and 90° of W in the ring of disc A, and with 20° of R and 120° of W in ring of disc B, the redness of the ring is hardly perceptible on B, but very distinct on A.Lest any one should criticise this observation on the ground of the unequal amounts of objective W mixed with the R and S of the rings, I made one more variation of the observation.
I put 90° of W and 20° of R and 250° of S in the ring on disc A, and the same amount of W and R and 8 in the ring of disc B. On rotation the ring on B appeared darker, of course, than the ring on A, and the R was very distinct in the ring on A, but in the ring on B it was hardly perceptible.
(I should add that in every case the colour of the rings was observed during fixation of a point on the edge of the ring or other fixed point.)
[Fig. 14. here - diagram giving examples of discs A and B]
In all these cases the R was less perceptible in the ring on the W ground than in the ring on the dark ground, and in every case the grey with which the R was mixed was decidedly a light grey, lighter than the hypothetical medium grey. Addition of contrast S to such a mixture should tend to increase the saturation of the R, because it brings the grey nearer to the medium grey, but it appears that the R becomes less rather than more saturated under the influence of the W ground. This is, I believe, due to direct inhibition of the R by the R element contained in the W light of the ground. The truth of this opinion I shall attempt to prove in the second part of this paper, but however this may be it is clear that the loss of saturation of R in the rings on W ground in my observations is not due to admixture of contrast S. It is in the highest degree probable that the loss of saturation of the R in Müller's experiment and in mine is due to the same cause, and is therefore not due to admixture of contrast S in the case of Muller's experiment as those who believe in a special S-process would have us suppose.' (94-96)
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Related toW.H.R. Rivers, 'The Photometry of Coloured Paper', Journal of Physiology 22 (1-2) (1897), pp. 137-145.
Description:'If a disc made up of coloured sectors is rotated so as to produce mixture in the ordinary way and a fine rod passed rapidly in front of the rotating disc, the rod will be seen to have following it a series of coloured bands corresponding to the colours of the sectors'. (137)
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