STUDIES IN SPECIAL SENSE PHYSIOLOGY 365 



image). This phase, which is the most striking part of the whole 

 experiment, produces the effect of a second bright object coming 

 behind the first, so that its appearance was termed " recurrent 

 vision " (Young, Davis), the " ghost " (Bidwell), or the " satellite " 

 (Hamaker). 



(4) The end of the satellite is not sharply defined and is followed 

 by another interval of darkness. 



(5) After this, the field once more brightens, and a faint bright 

 or homoiochromatic phase is obtained (of the same colour as the 

 original stimulus). If this part of the phenomenon be well de- 

 veloped, it is found that with a velocity such that the satellite is 

 distinct a bright haze fills the whole field, hence more then one 

 rotation should not be made. 



(6) Sixthly, and lastly, another dark interval occurs. 



It will be plain, even from this enumeration, that the phenomena 

 under consideration are by no means simple ; hence nobody will 

 be surprised to learn that divergences, even flat contradictions, 

 exist in the literature of the subject not merely as to the inter- 

 pretation of these results, but even as to their bona-fide existence. 

 I shall follow, for the most part, the lucid statement of the case 

 which we owe to Professor J. von Kries ( 17 ), indicating why I 

 believe his results to be reliable. 



With respect to the experiment as a whole, we have three 

 phases of illumination the primary image, the secondary or 

 satellite image, and the tertiary. In apparent brightness, these are 

 arranged in the order of their appearance. With low illuminations, 

 primary and secondary images alone are visible ; with still lower 

 intensities, the secondary also disappears. Further, the lengths 

 of the images can be made to vary, the dark intervals being lost. 

 Fixing our attention for a moment on the primary, we may note 

 the following points. Very frequently it exhibits a striped appear- 

 ance, similar to the well-known Charpentier " bands " ( 18 ) seen on 

 slow rotation of a white field containing a black sector. Apart 

 from this, it seems to the " light " eye uniformly bright. As, 

 however, dark adaptation proceeds, we find that the primary 

 image not only increases in extension and brightness, but with 

 chromatic stimuli ceases to be uniform. Thus, with blue light, 

 only the anterior border is deep blue, being followed by a white 

 stripe. Macdougall ( 19 ) finds this latter to commence at a distance 

 corresponding, in his experiments, to a time interval of iV second. 



