December 9, 1898.] 



SCIENCE. 



S-11 



As to contrast, the illustration here given 

 does not eshaustivel}' express the many 

 phases under which this principle appears. 

 Helmholtz has a theory of direction-coji- 

 trast, Heymans one of movement-contrast, 

 and Loeb one well illustrated by the case 

 just treated. Since, however, no one of 

 them contains in itself any reason for its 

 particular way of working, it becomes in 

 each case a mere name, a convenient ex- 

 pression only for the fact in hand. The 

 only legitimate application of the principle 

 of contrast is in those cases, well illustrated 

 by the circles of Ebbinghaus (Fig. 12), 



In the monograph already referred to 

 more than once AVundt powerfully emj)lia- 

 sizes the fact that the principle problem of 

 perspective is to determine whether its posi- 

 tion is primary or secondary ; whether, that 

 is, it is the caM.se of the illusion in a given 

 case or the effect of an already present illu- 

 sion. To determine this figures are found 

 with no accompanying perspective j^he- 

 nomena, though the nature of the illusion 

 is analogous to that presented by figures 

 with perspective phenomena. It would 

 seem, therefore, that perspective were wholly 

 secondary to some more fundamental factor. 



o°o 



o 

 o 



where two objectively-equal areas become 

 apparently diminished or enlarged respec- 

 tivelj', according as they are brought into 

 approximation with larger or smaller areas 

 of the same nature. In this sense of the 

 term the fact to which the principle is ap- 

 plied is brought into range with a multitude 

 of facts in every department of mental life, 

 the general law of which is that when any 

 mental state with certain prominent char- 

 acteristics is brought into comparison with 

 a second state of opposite characteristics 

 the peculiar quality of each is intensified, 

 just as a season of joy is more joyful when 

 immediately following a season of pain. 



And this presumption is strongly fortified 

 by the fact that the perspective phenome- 

 non is always unequivocal, that is, that di- 

 mension perceived as greater is always pro- 

 jected to the greater distance, and cannot 

 by any effort of ' imagination ' or ' will ' be 

 brought nearer. These few words give but 

 a faint hint of the force of the argumenta- 

 tion in detail. 



The physiological theory is the outcome of 

 an attempt to discover some principle that 

 shall be fundamental and hence capable of 

 universal application — valid, that is, not 

 only for 'variable' illusions of magnitude and 

 direction, but also for such ' constant' illu- 



