To sum up and state clearly the method of defining the brightness of the light in the following experiments: the candle-meter value of each light by which an electric-box was illuminated, as determined by the use of a Lummer-Brodhun photometer and measurements of the distance of the source of light from the filter, is given in connection with each of the experiments. This brightness value less the diminution caused by the passage of the light through a filter, which has been defined as to composition and thickness of the layer of solution, gives that degree of brightness by which the electric-box was illuminated. Tests of the dancer's ability to discriminate green and blue[1] in the transmitted light apparatus were made with four animals. An incandescent lamp marked 16-candle-power was set in each of the light-boxes. These lamps were then so placed that the green and the blue seemed to be of equal brightness to three persons who were asked to compare them carefully. Their candle-meter values in the positions selected were respectively 18 and 64, as appears from the statement of conditions at the top of Table 22. [Footnote 1: Hereafter the light transmitted by the blue-violet filter will be referred to for convenience as blue.] TABLE 22 GREEN-BLUE TESTS Brightnesses Equal for Human Eye Green 18 candle meters Blue 64 candle meters SERIES DATE NO. 10 NO. 11 1906 RIGHT WRONG RIGHT WRONG (GREEN) (BLUE) (GREEN) (BLUE) A and B[1] April 2 10 10 12 8 1 3 6 4 5 5 2 4 5 5 6 4 3 5 5 5 5 5 4 6 5 5 5 5 5 7 7 3 5 5 6 8 7 3 3 7 7 9 7 3 5 5 8 10 3 7 7 3 9 11 5 5 4 6 10 12 5 5 6 4 [Footnote: A single preference series of twenty tests.]