In another series the variant was the extent of surface exposed, the color-tone (neutral gray), outline, and other conditions being the same for both members of each pair.  The smaller figures were of the same area as those of the preceding series; in the larger figures this area was doubled.  Only one member of each pair is represented in the diagrams of this and the next series.

In a third series brightness was the variant, one member of each pair being white and the other gray (Bradley’s cool gray No. 2).  All other conditions were for both figures the same.

In still another series strips of granite-gray cardboard half a centimeter wide were cut out and pasted on black cards, some in straight and some in broken lines, but all of the same total length (10 cm.).  These were exposed under the same general conditions as those which have already been described, and were intended to show the relative effects of the two sorts of lines.

TABLE I.

1        2        3        4        5      Totals.   Averages. 
L   R    L   R    L   R    L   R    L   R    L    R    L     R
I. 45  45   25  29   27  27   31  24   36  20   164  145  32.8  29
II. 20  25   28  28   28  19   31  31   28  14   135  117  27    23.5
III. 11  12   17  28    0   7    0  15   27  23    55   85  11    17
IV.  7   6   47  22   17  21   17  45   31  30   119  124  23.8  24.8
V. 27  33   46  36   40  31   44  31   26  35   183  165  36.6  33.2
VI. 11  14   32  29   34  21   14  35    0  46    91  145  18.2  29
VII. 36  33   30  30   50  50   22  22   52  52   190  187  38    37.4
VIII. 41  44   33  33   45  45   34  44   37  28   190  194  38    38.8
IX. 45  45   39  46   42  47   47  47   44  44   217  229  43.4  45.8
X. 40  39   24  25   19  21   21  23   18  25   122  133  24.4  26.6
XI. 51  53   52  50   42  42   42  42   42  42   229  229  45.8  45.8

       334 349 373 356 344 331 303 359 341 359 1695 1754 30.8 31.9

    The Arabic numerals at the head of the columns refer, in every
    table, to the corresponding numerals designating the objects
    in the diagram accompanying the table.

    L:  left-hand object.
    R:  right-hand object.

The Roman numerals (I to XI) indicate the different subjects.  The same subjects appear in all the experiments, and under the same designation.  Two of the subjects, IV and VIII, are women.

The numbers under L and R denote the number of seconds during which the left-hand image and the right-hand image, respectively, were present in the period of introspection (60 seconds).

    General average:  L, 30.8 sec.; R, 31.9 sec.

[Illustration:  FIG. 1.]

Series No. 1.—­For the purpose of obtaining something that might serve as a standard of comparison, a series of observations was made in which the members of every pair were exact duplicates of each other, and were presented under exactly the same conditions, spatial position of course excepted.  The records of these observations are for convenience placed first as Table I.