Cited by C. Sherrington, 'Observations on 'flicker' in binocular vision', Proceedings of the Royal Society of London 71 (1902), pp. 71-76.

Cited by C.S. Sherrington, 'On Binocular Flicker and the Correlations of Activity of 'Corresponding' Retinal Points', Journal of Psychology 1 (1) (1904), pp. 26-60.
Description:

'A double sheet of thick milk-glass was observed by transmitted light given by a single-loop incandescent lamp, itself enclosed in a candle-shaped frosted glass. The lamp was fed a rather above its intended voltage, in order to give white quality of light, by accumulators unused during the experiment for any other purpose, and therefore supplying the lamp in constant measure. The lamp generally used was of 8 candle power, under a 100 volts. This lamp was set vertically in the axis of a rotating cylinder. This cylinder of turned brass was 78 mm. in diameter. In its side were cut three horizontal rows of rectangular windows tier above tier. The lamp though fixed in the axis of rotation of this revolving cylindrical screen was entirely free from all attachment to it. The milk-glass plate was fixed between the lamp and the inner face of the tiers of windows close to the latter.

Outside the moving cylindrical screen was a fixed semi- cylindrical screen concentric with the revolving one, and just wide enough to allow the inner revolving one to turn within it freely. In the fixed cylindrical screen four circular holes were arranged so that two are centred on the same horizontal line, and of the other two one was centred just so far above the left-hand hole of the just mentioned pair as the other is below the right-hand member of the pair. The horizontal distance between the centres of the right and left hand holes was 9 mm. The diameter of each hole was 8 mm. The vertical distance between the centres of the holes was exactly the same as that between the centres of tiers of the revolving cylindrical screen, namely 11 mm. These four circular holes in the outer fixed cylindrical screen were, in the experiments, viewed from a distance such that when the line of visual direction of the right eye passed through the centre of the right hole it met at the axis of the cylindrical lantern the line of visual direction of the left eye, which latter line passes through the centre of the left-hand hole.

This being so, the images of the lower left-hand hole and of the upper right-hand hole fused visually to singleness. They then appeared as the middle one of three arranged vertically one above the other.

A black vertical thin screen set at right-angles to the plane of the forehead was introduced between the eyes and the holes so as to screen from the left eye all view of the right-hand holes, and from the right eye all view of the left-hand holes. The distance of the eyes from the holes was in the observations on myself exactly 20cm. For some observers a little less was used, their interpupillar distance being less than my own.

The spindle of the revolving cylindrical screen was furnished with a step-pulley. Thence a rod ran to a step-pulley fixed on the spindle of an electro-motor. The speed of revolution of this motor was controlled by a set of coil-resistances, which served as a course adjustment, and by a fluid resistance in a trough 1 metre long, with a sliding electrode; this latter formed a fine adjustment. The speed of rotation of the cylindrical screen was recorded by marking the completion of each revolution of its spindle by an electro-magnetic signal writing on a travelling blackened surface, In the same surface the time was recorded by a writing clock marking fifths of seconds.

The inner revolving screen by its revolution opened and abscured alternately for equal periods the circular holes in teh fixed outer screen. The inner screen with its three tiers of windows was made in three pieces, each containing one tier of the windows. Thie piece containing the middle tier of openings was jointed in such a way that its openings could be set at any desired angular interval with the openings of the lowest tier. The highest tier was similarly jointed to the middle tier. In this way it could be arranged that the uppermost circular hole was open when the lower were closed, or was shut when the lower were closed, or was opened to any desired degree either before or after the lower.; further, by removing the top gallery of the rotating screen ot could be left permanently open. A similar relationship was also thus allowed between the middle holes and the lower.

By wearing weak prisms with their base-apex lines vertical the images of the right-hand and left-hand holes could be brought to the same horizontal levels. The right-eye prism was placed apex upward, the left-eye prism apex downward. The observer could then immediately fuse the four images to two by convergence. A horizontal fine thread halving each of the two middle holes, and similar but vertical threads halving the two other holes, serve to certify binocular vision to the observer. When the four holes were all allowed to act thus under appropriate convergent binocular gaze they were seen by the observer as two evenly lighted discs, one vertically above the other, and each cut into quadrants by a delicate black cross. By separately adjustable shutters any one, or any vertically edged fraction of one, of the discs caould be separately screened out of vision.

The observations required, (1) an operator to manage speed of motor, registration of time and revolution, &c., and (2) an observer, who seated in a dark compartment gave his sole attention to the watching of the illuminated discs. The observer had under his hand an electric key by which he could mark on the registering cylinder the moment at which under the conditions of increase or diminution of rotation rate the appearance of flicker began or ceased in the images of the discs under observation. The smoked registering cylinder was driven by a clockwork. The operator attending to it, and to the electric motor with its course and fine adjustments, and the chronograph marking fifths of seconds, was outside the dark compartment, in another room from that in which the person under observation sat, but the operator had the signal controlled by the person under observation, as also the signal of the speed-counter of the rotating shutter before him, and attended to their adjustment on the cylinder.

In making the observations the observer in the dark room fixed a minute thickening, marking the middle of each cross wire on the right- and left-hand discs. Besides the weak prisms he also wore artificial pupils between his eye and the prisms. The diameter of the artificial pupils was sometimes 3, sometimes 4mm. Both prisms and pupils were carried in a Landolt frame capable of both vertical and horizontal and also of angular adjustments.

Blackened aluminium side-flaps attached to the frame could be turned so as to block the field of either eye, obviating closure by the eyelid, which with some observers is liable to disturb the posture of the head. Fixation of the observers head was secured by a sodidly made wooden rest, supporting adjustable chin and forehead pieces.' (27-30)

 

Cited by C.S. Sherrington, The Integrative Action of the Nervous System (New Haven: Yale University Press, 1906).
Description:

A double sheet of thick milk-glass is observed by transmitted light given by a lamp. This lamp is set in the axis of a rotating cylinder (Fig. 76). In the side of the cylinder are three horizontal rows of rectangular windows, tier above tier. The lamp, though fixed in the axis of rotation of this revolving cylindrical screen, is entirely free from all attachment to it. The milk-glass plate is fixed between the lamp and the inner face of the tiers of windows, close to the latter.

Outside the moving cylindrical screen is a fixed semi- cylindrical screen concentric with the revolving one, and just wide enough to allow the inner revolving one to turn within it freely (Fig. 76). In the fixed cylindrical screen four circular holes are arranged so that two are centred on the same horizontal line, and of the other two one is centred just so far above the left-hand hole of the just mentioned pair as the other is below the right-hand member of the pair. The horizontal distance between the centres of the right and left hand holes is 9 mm. The diameter of each hole is 8 mm. The vertical distance between the centres of the holes is exactly the same as that between the centres of tiers of the revolving cylindrical screen, namely 1 1 mm. These four circular holes in the outer fixed cylindrical screen are, in the experiments, viewed from a distance such that when the line of visual direction of the right eye passes through the centre of the right hole it meets (Fig. 76) at the axis of the cylindrical lantern the line of visual direction of the left eye, which latter line passes through the centre of the left-hand hole.

This being so, the images of the lower left-hand hole and of the upper right-hand hole fuse visually to singleness. They then appear as the middle one of three arranged vertically one above the other.

A black vertical thin screen set at right-angles to the plane of the forehead is introduced (Fig. 77) between the eyes and the holes so as to screen from the left eye all view of the right-hand holes, and from the right eye all view of the left-hand holes.

The revolving screen is driven by an electromotor. The speed of revolution of this motor is controlled by a coarse ad- justment and by a fine adjustment The speed of rotation of the cylindrical screen is recorded by marking the completion of each revolution of its spindle by an electromagnetic signal writing on a travelling blackened surface (Fig. 77). On the same surface the time is recorded by a writing-clock marking fifths of seconds.

The inner revolving screen by its revolution opens and shuts alternately for equal periods the circular holes in the fixed outer screen. The inner screen with its three tiers of windows is made in three pieces, each containing one tier of the windows. The piece containing the middle tier of openings is jointed in such a way that its openings can be set at any desired interval with the openings of the lowest tier. The highest tier is similarly jointed to the middle tier. In this way it can be arranged that the uppermost circular hole is open when the lower ones are closed, or is shut when the lower are closed, or is opened to any desired degree either before or after the lower; further, by removing the top gallery of the rotating screen it can be left permanently open. A similar relationship is also allowed between the middle holes and the lower.

By wearing weak prisms with their base-apex lines vertical the images of the right-hand and left-hand holes can be brought to the same horizontal levels. The observer can then immediately fuse the four images to two by convergence. A horizontal fine thread halving each of the two middle holes, and similar but vertical threads halving the other two holes, serve to certify binocular vision to the observer. When the four holes are all allowed to act thus under appropriate convergent binocular gaze they are seen by the observer as two evenly lighted discs, one vertically above the other, and each cut into quadrants by a delicate black cross. By separately adjustable shutters any one, or any vertically edged fraction of one, of the discs can be separately screened out of vision.' (357-361)