As in the experiment with the dumb-bell, we have also here three cases:  the control, the case of the eye moving, and again a control.

Case 1. T swings with the pendulum. I is placed in the front groove, and the eye looks straight forward without moving.  The pendulum falls from 9.5 deg. at one side, and the illumination is so adjusted that the phase in which the band is reddish-orange, is unmistakably perceived before that in which it is straw-yellow.  The appearance must be 3 followed by 5 (Fig. 8).

Case 2. T is fixed in the background, I on the pendulum, and the phenomena are observed with the eye moving.

Case 3.  A repetition of case 1, to make sure that no different adaptation or fatigue condition of the eye has come in to modify the appearance of the two successive phases as at first seen.

The possible appearances to the moving eye are closely analogous to those in the dumb-bell experiment.  If the eye moves too soon or too late, so that it is at rest during the exposure, the image is like T itself (Fig. 8) but somewhat fainter and localized midway between the points P and P’.  If the eye moves reflexly at the rate of the pendulum, the image is of the shape i and shows the two phases (3 followed by 5).  It is localized in the middle and appears to move across the nine-centimeter opening.

A difficulty is met here which was not found in the case of the dumb-bell.  The eye is very liable to come to a full stop on one of the colored surfaces, and then to move quickly on again to the final fixation-point.  And this happens contrary to the intention of the subject, and indeed usually without his knowledge.  This stopping is undoubtedly a reflex process, in which the cerebellar mechanism which tends to hold the fixation on any bright object, asserts itself over the voluntary movement and arrests the eye on the not moving red or green surface as the exposure takes place.  A comparable phenomenon was found sometimes in the experiment with the dumb-bell, where an eye-movement commenced as voluntary would end as a reflex following of the pendulum.  In the present experiment, until the subject is well trained, the stopping of the eye must be watched by a second person who looks directly at the eye-ball of the subject during each movement.  The appearances are very varied when the eye stops, but the typical one is shown in Fig. 8:1.  The red strip AB is seldom longer and often shorter than in the figure.  That part of it which is superposed on the green seldom shows the orange phase, being almost always of a pure straw-yellow.  The localization of these images is variable.  All observations made during movements in which the eye stops, are of course to be excluded.