370 TITCHENER AND PYLE— ON THE AFTER-IMAGES [July 23, 



We made no long series of tests, since the question at issue had 

 already been answered, so far as we could answer it, by the follow- 

 ing Exps. II.-V. The experiments were, however, carefully con- 

 ducted. The work was done in a long gray-tinted light-optics room, 

 with achromatic adaptation; the observers were the writers (T, P), 

 Mr. L. R. Geissler {G), assistant in psychology, and two unprac- 

 tised students, Mrs. G. L. de Ollogni and Mr. E. M. Stevens ; and 

 the experimenter had acquired great skill, from Exps. II. and IV., 

 in moving the wedge slowly and steadily forward. In general, the 

 stimulus-background was black, and the field for the projection of 

 the after-image was white, though these relations were occasionally 

 changed. 



As we had expected, there was no trace of color in the after- 

 image; this result was uniform. In control experiments, in which 

 (after a period for the recovery of the eye) the glass was exposed 

 for 30 sec. at the point finally reached in the adaptation experiments, 

 the after-image showed a brief period of dirty orange or brownish 

 yellow, followed by gray. 



Experiment II.: The Marbe Color Mixer. — The observations 

 with Tschermak's wedge could not, in any case, be regarded as more 

 than preliminary. For systematic work we employed, first, the 

 Marbe color mixer, which permits the change of a colored sector 

 during rotation of its discs, and thus gives scope for progressive 

 adaptation. 



The observer, head in rest, was seated at a distance of i m. from 

 a black cardboard screen. The rotating discs were observed 

 through a circular opening, 2 cm. in diameter, cut in the screen at 

 the level of the eyes. The observation was monocular, and was 

 continued for 5 to 7 min. The discs were made up of white, with 

 a sector of colored paper (Zimmermann R, Y, G, B, V) ; the color 

 at the outset was subliminal for the achromatically light-adapted 

 eye, and was gradually increased in amount as the observation pro- 

 ceeded. The after-image was projected upon a fixation-point 

 marked on a white cardboard dropped in front of the black screen.' 



' For comparative purposes, a few observations were taken with a gray 

 screen, and with projection upon a black or gray background. Nothing new 

 resulted. 



