SENSATION. 21 



steady fixation, and. have failed to properly account for the 

 various modifying influences which have been mentioned 

 above. We can easily establish this if we examine the most 

 striking experiments in simultaneous contrast. 



Of these one of the best known and most easily arranged 

 is that known as 3Ieyers experiment. A scrap of gray paper 

 is placed on a colored background, and both are covered 

 by a sheet of transparent white paper. The gray spot then 

 assumes a contrast-color, comj)lementary to that of the 

 background, which shines with a whitish tinge through the 

 paper which covers it. Helmholtz explains the phenome- 

 non thus : 



" If the background is green, the covering-paper itself appears to be 

 of a greenish color. If now the substance of the paper extends without 

 appai'ent interruption over the gray which lies under it, we think that 

 we see an object glimmering through the greenish paper, and such an 

 object must in turn be rose-red, in order to give white light. If, how- 

 ever, the gray spot has its limits so fixed that it appears to be an inde- 

 pendent object, the continuity with the greenish portion of the surface 

 fails, and we regard it as a gray object which lies on this surface. " * 



The contrast-color may thus be made to disappear by 

 tracing in black the outlines of the gray scrap, or by j)lac- 

 ing above the tissue paj)er another gray scrap of the same 

 degree of brightness, and comparing together the two grays. 

 On neither of them does the contrast-color now apj^ear. 



Hering t shows clearly that this interpretation is incor- 

 rect, and that the disturbing factors are to be otherwise 

 explained. In the first place, the experiment can be so 

 arranged that we could not possibly be deceived into be- 

 lieving that we see the gray through a colored medium. 

 Out of a sheet of gray paper cut strips 5 mm. wide in such 

 a way that there will be alternateh- an empty space and a 

 bar of gray, both of the same width, the bars being held to- 

 gether by the uncut edges of the gray sheet (thus presenting 

 an appearance like a gridiron). Lay this on a colored back- 

 ground — e.g. green — cover both with transparent paper, 

 and above all put a black frame which covers all the edges, 

 leaving visible only the bars, which are now alternately 



* Helmholtz, Physiolog. Optik, p. 407. 



f In Archiv f. d. ges. Physiol., Bd. XLi. G. 1 II. 



