ge falls full on the
fovea. But one streak, and that the correctly localized one, is seen.
This is like case 2, except that here the streak extending from _L_ to
the right quite reaches the final fixation-point _B'_. It is therefore
not the fact of a stimulation being foveal which conditions its being
seen in two places.

It should be added that this experiment involves no particular
difficulties of observation, except that in case 4 the eye tends to
stop midway in its movement when the spot of light _L_ comes in view.
Otherwise no particular training of the subject is necessary beyond
that needed for the observing of any after-image. Ten persons made the
foregoing observations and were unanimous in their reports.

This experiment leaves it impossible to doubt that the conjecture of
Schwarz, that the correct image is only the false one seen over again,
is perfectly true. It would be interesting to enquire what it is that
conditions the length of the false streak. It is never more than one
third that of the correct streak (Fig. 3:1; except of course under the
artificial conditions of Fig. 3:3) and may be less. The false streak
seems originally to _dart out_ from the light, as described by Lipps,
visibly growing in length for a certain distance, and then to be
suddenly eclipsed or blotted out _simultaneously_ in all its parts.
Whereas the fainter, correct streak flashes into consciousness _all
parts at once_, but disappears by fading gradually from one end, the
end which lies farther from the light.

Certain it is that when the false streak stops growing and is
eclipsed, some new central process has intervened. One has next to
ask, Is the image continuously conscious, suffering only an
instantaneous relocalization, or is there a moment of central
anaesthesia between the disappearance of the false streak and the
appearance of the other? The relative dimness of the second streak in
the _first moment_ of its appearance speaks for such a brief period of
anaesthesia, during which the retinal process may have partly subsided.

We have now to seek some experimental test which shall demonstrate
definitely either the presence or the absence of a central anaesthesia
during eye-movements. The question of head-movements will be deferred,
although, as we have seen above, these afford equally the phenomenon
of twice-localized after-images.

IV. THE PENDULUM-TEST FOR ANAESTHESIA.

A. Apparatus must be devised to fulfil the fo