field presents.  The two eyes do not, of course, function separately in such a case, and the difference in the two sets of results is undoubtedly due to the influence of movements in the closed eye upon that which is open; or rather, to the difference in binocular functioning caused by shutting off the visual field from one eye.  The former expression is justified in so far as we conceive that the tendency of the closed eye to turn slightly upward in its socket affects also the direction of regard in the open eye by attracting toward itself its plane of vision.  But if, as has been pointed out, this elevation of the line of sight in the closed eye is accompanied by a characteristic change in the process of binocular convergence, the result cannot be interpreted as a simple sympathetic response in the open eye to changes taking place in that which is closed, but is the consequence of a release of convergence strain secondarily due to this act of closing the eye.

Several points of comparison between judgments made with binocular and with monocular vision remain to be stated.  In general, the process of location is more uncertain when one eye only is used than when both are employed, but this loss in accuracy is very slight and in many cases disappears.  The loss in accuracy is perhaps also indicated by the range of variation in the two cases, its limits being for binocular vision +46’.29 to -56’.70, and for monocular +62’.30 to -61’.10, an increase of 20’.41.  In the darkened room similar relations are presented.  The mean variations are as follows:  binocular vision, 31’.42; monocular, 32’.17.  Its limits in individual judgments are:  binocular, -1’.62 to -128’.70, monocular, +66’.38 to -71’.06, an increase of 10’.36.  In all ways, then, the difference in accuracy between the two forms of judgment is extremely small, and the conclusion may be drawn that those significant factors of judgment which are independent of the figuration of the visual field are not connected with the stereoscopic functioning of the two eyes, but such as are afforded by adjustment in the single eye and its results.

VI.

The experimental conditions were next complicated by the introduction of abnormal positions of the eyes, head and whole body.  The results of tipping the chin sharply upward or downward and keeping it so fixed during the process of location are given in the following table, which is complete for only three observers: 

TABLE VIII.

Observer.              Upward Rotation.            Downward Rotation. 
C.E.      A.D.      M.V.       C.E.      A.D.      M.V.
L (50)         +43.98    43.98     5.62     +28.32   28.32    5.02
K (50)         -33.72    33.72    71.33     +19.49   19.49   55.22
L (20)         -39.10    45.90    33.60     -68.65   69.25   25.20
Average:          — 9.61    41.20    36.85     -19.94   39.02   28.48
Normal:           -64.14    67.08    33.51

The results of rotating the whole body backward through forty-five and ninety degrees are given in the following table: