objects, that is, as something discontinuous.  Where does the factor of discontinuity come in?  If we suppose the retinal disturbance to produce a continuous sensation in consciousness, we should expect, according to every analogy, that this sensation would be referred to one continuously existing object.  And if this object is to be localized in two places successively, we should expect it to appear to move continuously through all intervening positions.  Such an interpretation is all the more to be expected, since, as the strobic phenomena show, even discontinuous retinal processes tend to be interpreted as continuously existing objects.

On the other hand, if there were a central anaesthesia during eye-movement, the continuous process in the retina could not produce a continuous sensation, and if the interval were long enough the image might well be referred to two objects; since also, in the strobic appearances, the stimulations must succeed at a certain minimal rate in order to produce the illusion of continuous existence and movement.

This consideration seemed to make it worth while to perform some experiments with the falsely localized after-images.  The phenomenon had also by chance been noted in the case of the eye moving past a luminous dot which was being regularly covered and uncovered.  The appearance is of a row of luminous spots side by side in space, which under conditions may be either falsely or correctly localized.  Since these dots seemed likely to afford every phenomenon exhibited by the streaks, with the bare chance of bringing out new facts, apparatus was arranged as in Fig. 1, which is a horizontal section.

DD is a disc which revolves in a vertical plane, 56 cm. in diameter and bearing near its periphery one-centimeter holes punched 3 cm. apart. E is an eye-rest, and L an electric lamp. SS is a screen pierced at H by a one-centimeter hole.  The distance EH is 34 cm.  The disc DD is so pivoted that the highest point of the circle of holes lies in a straight line between the eye E and the lamp L.  The hole H lies also in this straight line.  A piece of milk-glass M intervenes between L and H, to temper the illumination.  The disc DD is geared to a wheel W, which can be turned by the hand of the observer at E, or by a second person.  As the disc revolves, each hole in turn crosses the line EL.  Thus the luminous hole H is successively covered and uncovered to the eye E; and if the eye moves, a succession of points on the retina is stimulated by the successive uncovering of the luminous spot.  No fixation-points are provided for the eye, since such points, if bright enough to be of use in the otherwise dark room, might themselves produce confusing streaks, and also since an exact determination of the arc of eye-movement would be superfluous.

[Illustration:  Fig. 1.]