Jean Théophile Desaguliers (1683-1744) and eighteenth century vision research

The emergence of psychology as an empirical discipline was influenced to a great extent by experimental investigations of visual phenomena, particularly in the nineteenth century. Less attention has been paid to experimental enquiries conducted in the eighteenth century, especially those of Jean Théophile Desagliers (1683-1744). He was an ardent advocate of Newtonian optics, on which he lectured and gave demonstrations. His research on colour and binocularity is outlined, together with those of other students of vision in that century. Experiments on visual vertigo conducted at the end of the century are also described. In 1716 Desaguliers reported a method of binocular combination that became widely employed in other studies of binocular vision, namely, placing an aperture in such a position that two more distant, adjacent objects were in the optical axes of each eye. Under these circumstances red and green patches of silk did not mix after the manner of combining prismatic lights, but engaged in rivalry. Desaguliers also investigated size perception and showed that apparent size was determined by apparent distance rather than physical distance. Moreover, he did not base his conclusions on his own observation but on those of 'any unprejudic'd Person'. Thus, both stimulus control and the use of the unbiased observer were employed in eighteenth century experimental studies of vision.