of the image of _i_ at all moments of the exposure.

[Illustration: PSYCHOLOGICAL REVIEW. MONOGRAPH SUPPLEMENT, 17. PLATE PLATE II.
Fig. 4. Fig. 6.
HOLT ON EYE-MOVEMENT.]

Thus much of preliminary discussion to show how, by means of a
pendulum, identical stimulations can be given to the moving and to the
resting eye. We return to the problem. It is to find out whether a
stimulation given during an eye-movement can be perceived if its
after-image is so brief as wholly to elapse before the end of the
movement. If a period of anæsthesia is to be demonstrated, two
observations must be made. First, that the stimulation is bright
enough to be _unmistakably visible_ when given to the eye at rest;
second, that it is not visible when given to the moving eye. Hence, we
shall have three cases.

Case 1. A control, in which the stimulation is proved intense
enough to be seen by the eye at rest.

Case 2. In which the same stimulation is given to the eye
during movement.

Case 3. Another control, to make sure that no change in the
adaptation or fatigue of the eye has intervened during the
experiments to render the eye insensible to the stimulation.

Fig. 5 shows the exact arrangement of the experiment. The figure
represents a horizontal section at the eye-level of the pendulum of
Fig. 4, with accessories. _E_ is the eye which moves between the two