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.

With these two precautions taken, the image on the final
fixation-point is like either 3, 4, or 5. Shape 5 very rarely appears,
while the trained subject sees 4 and 3 each about one half the times;
and either may be seen for as many as fifteen times in succession.

Shape 4 is of course exactly the appearance which this experiment
takes to be crucial evidence of a moment of central anaesthesia, before
the image is perceived and during which the stimulation of the handle
_h_ completely elapses. Eight subjects saw this phenomenon distinctly
and, after some training in timing their eye-movements, habitually.
The first appearance of the handleless image was always a decided
surprise to the subject (as also to the writer), and with some
eagerness each hastened to verify the phenomenon by new trials.

The two ends (_e_, _e_)