The change presented by the constant error can here be interpreted
only speculatively. I believe it is a frequently noted fact that the
lights in a distant house or other familiar illuminated object on
land, and especially the signal lights on a vessel at sea appear
higher than their respective positions by day, to the degree at times
of creating the illusion that they hang suspended above the earth or
water. This falls in with the experimental results set forth in the
preceding table. It cannot be attributed to an uncomplicated tendency
of the eyes of a person seated in such a position to seek a lower
direction than the objective horizon, when freed from the corrective
restraint of a visual field, as will be seen when the results of
judgments made in complete darkness are cited, in which case the
direction of displacement is reversed. The single illuminated spot
which appears in the surrounding region of darkness, and upon which
the eye of the observer is directed as he makes his judgment, in the
former case restricts unconscious wanderings of the eye, and sets up a
process of continuous and effortful fixation which accompanies each
act of determination. I attribute the depression of the eyes to this
process of binocular adjustment. The experience of strain in the act
of fixation increases and decreases with the distance of the object
regarded. In a condition of rest the axes of vision of the eyes tend
to become parallel; and from this point onward the intensity of the
effort accompanying the process of fixation increases until, when the
object has passed the near-point of vision, binocular adjustment is no
longer possible. In the general distribution of objects in the visual
field the nearer, for the human being, is characteristically the
lower, the more distant the higher, as one looks in succession from
the things at his feet to the horizon and _vice versa_. We should,
therefore, expect to find, when the eyes are free to move in
independence of a determinate visual field, that increased convergence