In order to separate the resident organic factors from those presented by the fixed relations of the external world, an adaptation of the mechanism was made for the purpose of carrying on the observations in a darkened room. For the cardboard disc was substituted a light carriage, riding upon rigid parallel vertical wires and bearing a miniature ground-glass bulb enclosing an incandescent electric light of 0.5 c.p. This was encased in a chamber with blackened surfaces, having at its center an aperture one centimeter in diameter, which was covered with white tissue paper. The subdued illumination of this disc presented as nearly as possible the appearance of that used in the preceding series of experiments. No other object than this spot of moving light was visible to the observer. Adjustment and record were made as before. The results for the same set of observers as in the preceding case are given in the following table: TABLE II. Subject. Constant Error. Average Deviation. Mean Variation. _A_ (50) - 52.76 55.16 30.08 _C_ (30) - 7.40 42.00 35.31 _D_ (50) - 14.24 38.60 30.98 _E_ (50) - 43.12 86.44 30.19 _F_ (100) - 2.01 72.33 20.27 _G_ (100) - 21.89 47.47 32.83 _H_ (50) - 1.62 59.10 29.95 _I_ (50) - 32.76 41.60 24.40 _K_ (50) - 61.70 100.02 52.44 _L_ (40) -128.70 128.90 27.83 Average: - 36.62 67.16 31.43