December 9, 1898.] 



SCIENCE. 



825 



the position indicated in the figure in order 

 to appear continuous with a. The lines 

 emploj'ed may be narrow strips of black 



cardboard, or the lines may be replaced by 

 coins or other objects of a similar nature. 

 The discoverer's explanation is given in 

 terms of contrast. If the space value of the 

 impression h be the apparent distance of h 

 from M we may say that this has been in- 

 creased by the presence of c, since the re- 

 sulting retinal impressions come now into 

 the relation of ' contrast,' or of mutual re- 

 pulsion, whereby the space value of h is in- 

 creased. Accordingly b must be moved 

 nearer to M, that its apparent space value 

 may be equal to that of a. This explana- 

 tion has not met with universal favor, and 

 Hej^mans, Filehne and Wnndt have each 

 sought other solutions. The first attempts 

 to unite this to the Zollner illusion, the 

 second to explain in terms of perspective. 

 Wundt, in opposition to all previous at- 

 tempts, points out the fact that this is an illu- 

 sion of indirect vision, to be explained, there- 

 fore, only by reference to some known facts in 

 that field. These facts he finds in the well 

 known illusion of yon Recklinghausen, in 

 accordance with which rows of apparently 



horizontal and vertical points, placed far- 

 ther and farther outwards from the point of 

 fixation and in apf)arent parallelism with 

 the real horizontal and vertical passing 

 through this point, must be made to curve 

 slightly with the convex side towards the 

 point of fixation. In the illusion of Loeb 

 h alone can be placed correctly in line with 

 a, since the impression made by the lines is 

 sufliciently strong to overcome the tendency 

 to the Recklinghausen illusion. The ad- 

 dition of c restores the normal conditions 

 somewhat, however, perhaps through the 

 impression of imaginary lines drawn from 

 a to 6 and c ; and the expected inward in- 

 clination from a to 6 now takes place. That 

 Wundt' s explanation is wholly clear can by 

 no means be asserted. Still, the full recog- 

 nition of the fact that this is an illusion of 

 indirect vision, and the attempt to subsume 

 this under phenomena already known, are 

 long steps towards a possible explanation 

 that may prove more satisfactory. 



6 and 7. The Illusions of Baldwin and 

 Judd. — At the last meeting of the Amer- 

 ican Psychological Association, held during 

 the Christmas holidays, two reports were 

 made in reference to recently observed 

 optical illusions. Professor Baldwin gave 

 some new observations made upon the illu- 

 sion of Fig. 11, with which the readers of 

 Science were made acquainted through 

 these colums in 1896. The jjoint actually 

 midway between the circumferences of the 

 two circles seems nearer the larger. So 

 far as the writer is aware, no final expla- 

 nation has as yet been proposed. In the 

 report referred to we are simply told that 

 perspective ' has probably little influence,' 

 and that the principle of ' equilibrium' can- 

 not account for it, since the placing of the 

 apparent middle point is in the contrary di- 

 rection to that demanded by this principle. 

 The announcement of further experimental 

 results is awaited with interest. Dr. Judd 

 has called attention to an interesting illu- 



