It is several years since I first observed and instituted some experiments with an interesting color conversion phenomenon which, so far as I could learn, had previously been unobserved.
After some thought and examination regarding the phenomenon I communicated it to Dr. George T. Ladd, professor of philosophy in Yale University, who, in connection with Prof. E. W. Scripture made some observations in the Yale psychologic laboratory. In Prof. Ladd's report of these joint observations1 the elements of the appearance were not fully stated and no contribution to the elucidation of its nature or causes was made. I have improved the first opportunity of leisure which has been presented to me for a study of the interesting phenomenon and now present a description with a statement of some of the principles involved in its explanation.
THE PHENOMENON DESCRIBED.
If, in the midst of a somewhat broadly extended surface of