The Singular Vision of William Charles Wells (1757–1817)

Abstract

William Charles Wells retained an interest in vision throughout his life. His first book was on single vision with two eyes; he integrated vision and eye movements to determine principles of visual direction. On the basis of experiments and observations he formulated three principles of visual direction, which can readily be demonstrated. In the course of these studies, he also examined visual acuity, accommodation and convergence, visual persistence, and visual vertigo. Insights into visual processing were mainly derived from observations of afterimages that were used to provide an index of how the eyes moved. His experiments enabled him to distinguish between the consequences of active and passive eye movements (later called outflow and inflow) as well as describing nystagmus following body rotation. After providing a brief account of Wells's life, his neglected research on vision is described and assessed.

Keywords:

• single vision
• accommodation
• eye movements
• visual acuity
• visual motion
• William Charles Wells

Notes

¹What we refer to as “ocular line” is termed “visual line” in modern terminology. In our view, the term “visual line” is unfortunate because it denotes the physical line and not the perceptual as in “visual direction” or “visual distance.” Also, the term “optic” axis now refers to the axis of an eye as an optical instrument (i.e., a line joining “the anterior and the posterior pole of the eyes, the cardinal points of the dioptric system and the centre of rotation of the eye ball” [Martin, 1942, p. 39]). Henceforth, we will use the term ocular axis for Wells's (1792) term “optic axis” (when it is not a direct quotation) and “ocular line” for visual line.