centers.  It seems to consist in a rapid succession of small reflex innervations, and is very different from the type of movement in which one definite innervation carries the eye through its 42 deg., and which yielded the phenomena with the perimeter.  A subject under the spell of this reflex must be exercised in innervating his eye to move from P to P’ and back in single, rapid leaps.  For this, the pendulum is to be motionless and the eye is not to be stimulated during its movement.

[20] Exner, Sigmund, Zeitschrift f.  Psychologie u.  Physiologie der Sinnesorgane, 1896, XII., S. 318.  ’Entwurf zu einer physiologischen Erklaerung der psychischen Erscheinungen,’ Leipzig u.  Wien, 1894, S. 128.  Mach, Ernst, ’Beitraege zur Analyse der Empfindungen,’ Jena, 1900, S. 98.

These two cases in which the image is localized midway between P and P’ interest us no further.  Localized on the final fixation-point, the image is always felt to flash out suddenly in situ, just as in the case of the ‘correctly localized’ after-image streaks in the experiments with the perimeter.  The image appears in one of four shapes, Fig. 7:  2 or 3, 4 or 5.

First, the plain or elongated outline of the dumb-bell appears with its handle on the final fixation-point (2 or 3).  The image is plain and undistorted if the eye moves at just the rate of the pendulum, elongated if the eye moves more rapidly or more slowly.  The point that concerns us is that the image appears with its handle.  Two precautions must here be observed.

The eye does not perhaps move through its whole 42 deg., but stops instead just when the exposure is complete, that is, stops on either O or N and considerably short of P or P’.  It then follows that the exposure is given at the very last part of the movement, so that the after-image of even the handle h has not had time to subside.  The experiment is planned so that the after-image of h shall totally elapse during that part of the movement which occurs after the exposure, that is, while the eye is completing its sweep of 42 deg., from O to P, or else from N to P’.  If the arc is curtailed at point O or N, the handle of the dumb-bell will of course appear.  The fact can always be ascertained by asking the subject to notice very carefully where the image is localized.  If the eye does in fact stop short at O or N, the image will be there localized, although the subject may have thoughtlessly said before that it was at P or P’, the points he had nominally had in mind.

But the image 2 or 3 may indeed be localized quite over the final fixation-point.  In this case the light is to be looked to.  It is too bright, as it probably was in the case of Dodge’s experiments.  It must be further reduced; and with the eye at rest, the control (case I) must be repeated.  In the experiments here described it was always found possible so to reduce the light that the distinct, entire image of the dumb-bell (2, Fig. 7) never appeared localized on the final fixation-point, although in the control, H, of Fig. 7:1, was always distinctly visible.