Quantitative visual psychophysics during the period of European enlightenment. The studies of the astronomer and mathematician Tobias Mayer (1723-1762) on visual acuity and colour perception.

During the sixth decade of the 18th century, Tobias Mayer, Professor of Astronomy and Applied Mathematics (Economy) at the University of Göttingen, performed two investigations on quantitative visual psychophysics. He deduced a power law for the dependence of visual acuity on the intensity of light by which the stimulus pattern was illuminated. In his measurements he compared visual acuity determined with single black dots and visual acuity measured with gratings or checkerboard patterns; the latter he considered as the "real" measurement of visual acuity. Mayer also developed a three-dimensional hexaedric colour space from the definition of subtractive colour mixtures of three primary pigments (red, yellow, blue). This colour space can be considered as the predecessor of the later colour tables of Ostwald and Munsell. Mayer gave a simple quantitative description of each of the 819 hues in his colour space. Both psychophysical studies developed out of Mayer's interest in practical problems in astronomy and cartography. Mayer's main scientific merits were in the field of astronomy and mathematical geography. His psychophysical studies were performed in the spirit of enlightenment with the a priori assumption that the performance of the human perceptual machinery can be measured quantitatively and that the results are adequately expressed by mathematical rules. Mayer's achievements in the fields of mathematics, physics, astronomy and cartography were recently summarized by the extensive historical research of G.F. Forbes. In the present report a short biographical note precedes the description of Mayer's psychophysical studies.