332 w. MCDOUGALL : 5. Passive : 22a = 8", 216 = 8", flat = 102". In this table passive means that throughout the period of 118 seconds the subject maintains as far as possible the atti- tude of a passive spectator of the changes ; holding a means that he made efforts to recall that form of the cube of which the angle a appears as the most prominent point whenever the figure appeared in any other form, and endeavoured to keep that form present to consciousness as long as possible ; holding b means that throughout 118" he made similar efforts to favour the predominance in consciousness of the other form of cube in which the angle b appears as the most prominent point of the figure, while flat means the sum of those periods during which the figure appears merely as a group of lines on a flat surface. The continuous fixation of the central point of the figure about which the whole figure is symmetrically arranged pre- vents any lateral movements of the eyes which might favour the predominance of either form of cube and ensures also that any changes of accommodation shall not favour the pre- dominance of one form over the other. Muscular factors seem thus to be eliminated, yet the influence of volition in favouring the predominance of either form of cube appears distinctly enough in the figures of the table which denote the sums of the periods during which each form was present to consciousness, though it is not very great. In some ex- periments made when I was quite fresh I attained more marked effects of this sort, in others, when fatigued, less distinct effects. I found the needful effort to be very severe and exhausting. Another subject who repeated these ex- periments had much greater success in voluntarily favouring predominance of one form of cube under these conditions. He was able to favour the predominance of the one form to the almost complete exclusion of the other, so that the appearance of one form of cube alternated with periods in which the figure appeared flat or confused. This he achieved by imagining the cube to be a square box into the open end of which he imagined himself to toss balls continuously. The groupings of the white discs of fig. 2 (p. 335) may also be made to succeed one another in any desired order by voluntary efforts while one point is continuously fixated, and in this case the slightest wavering of the fixation is at once revealed by the appearance of bright edges to the discs. The grouping may also be changed at will in the after-image pro- jected upon a grey surface, while eye-movements are excluded by fixation of a point on that surface. Under these conditions
