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Creator (Definite): Adolph-Moïse Bloch
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NB: A translation of this article can be found in A. Gorea, 'A refresher of the original Bloch’s Law paper (Bloch, July 1885)', i-Perception (2015).
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Cited byT. Quick, 'Disciplining Physiological Psychology: Cinematographs as Epistemic Devices, 1897-1922', Science in Context 30 (4), pp. 423-474.
Description:'In 1885, Marey's associate Adolph-Moïse Bloch adapted a version of the intermittently-obscured lamps that William Henry Fox Talbot and Simon von Stampfer had developed during the 1830s to physiological investigation. Where Talbot sought to measure light intensity itself, Bloch sought to establish a law regarding the rates at which individual sensation-flashes produced a continuous light-sensation under different conditions (Bloch 1885, 493-495; Schickore 2006, 254-255). Such studies prompted a range of physiological investigations into Stampfer's "stroboscopic" effects during the 1890s (e.g. Charpentier 1890; Schenck 1896; Marbe 1898).' (454)
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Related toMaterial relating to the development and use of stroboscopes before c.1910
Description:Raises question of whether or not it is possible to pass a light in front of the eye without it being seen.
Notes that a certain number of physiologists have addressed this question, and that it has finally been answered in the affirmative by M.M. Richet and Bréguet. Considers however that their results are ‘qualitative’, and that it would therefore be desirable to ‘spécifier exactement la durée de l'excitation visuelle, comme aussi l'intensité de cette excitation.’ (493)
Uses Foucault regulator to produce regular movement.
The regulator is combined with a box with slits cut into it, with a candle placed in front. Revolution of the box is measured by the regulator - this allows Bloch to estimate the length of time that the candle is visible for as the slots pass in front of it. Moments of illumination are observed through a metre-long copper tube, the end of which being blocked off except for a 0.5mm-wide pinhole.
Obtains result that duration required for the spark to remain unnoticed is 1/1119th of a second.
Varies brightness of light, duration of passage of slots to determine whether there is a law relating to the relation between intensity of light and speed of rotations needed to make light unnoticeable.
Concludes that ‘pour une lumière double, il faut une durée moitié moindre, si on veut arriver à la cessation de la sensation visuelle.’ (495)
