slow continuous change in the position of the illuminated spot, no
such wandering of the eye from its original point of regard occurs,
and the spot does not float. The rate at which such objective
movements may take place without awareness on the part of the observer
is surprisingly great. Here the fatigue due to sustained fixation is
obviated by the series of rapid and slight sensory reflexes which take
place; these have the effect of keeping unchanged the retinal
relations of the image cast by the illuminated spot, and being
undiscriminated in the consciousness of the observer the position of
the point of regard is apprehended by him as stationary. The
biological importance of such facile and unconscious adjustment of the
mechanism of vision to the moving object needs no emphasis; but the
relation of these obscure movements of the eyes to the process of
determining the plane of the subjective horizon should be pointed out.
The sense of horizontality in the axes of vision is a transient
experience, inner conviction being at its highest in the first moments
of perception and declining so characteristically from this maximum
that in almost every case the individual judgment long dwelt upon is
unsatisfactory to the observer. This change I conceive to be a
secondary phenomenon due to the appearance of the visual wanderings
already described.


VIII.


The influence of sensory reflexes in the eye upon the process of
visual orientation was next taken up in connection with two specific
types of stimulation. At top and bottom of the vertical screen were
arranged dark lanterns consisting of electric bulbs enclosed in