32 EOYAL SOCIETY OF CANADA 



128. The writer can see the phenomenon described by him, under 

 certain conditions, and, as shown in the curves, Plate I, the oscillations 

 are quicker in light than in darkness. There, therefore, seems to be 

 some connection between these phenomena, although there are cer- 

 tainly decided points of difference, especially with regard to motion. 

 Not having seen the phenomenon described by Pur kin je, I can make no 

 distinct comparison. 



, 129. Such, however, is not the case with the following phenomena, 

 described by Helmholtz,^ for the writer has observed this distinctly (as 

 nearly every one can) and can note no resemblance between it and the 

 phenomenon described by him. The paragraph in Helmholtz referred 

 to runs as follows : — " Bright moving points appear in the visual fiield 

 if one intently 'fixes' a large, regularly illuminated surface {e.g., the 

 heavens, or snow fields) especially during vigorous walking or other 

 exercise. The points spring from different parts of the visual field, 

 and continue to move quite quickly in very different paths which are, 

 on the whole, not quite straight. There appears also upon the path 

 which one point has taken, new points following the same path, etc." 



130. Neither must the phenomenon described in this paper " as 

 first seen " be confounded ^dth the phenomenon described by A. Konig,^ 

 for the writer has observed the Konig-phenomenon several times, and 

 can note no resemblance. The hexagons, described by Konig as being 

 visible upon awaking and before opening the eyes in a half-darkened 

 room, are very much lai-ger than those described (par. 4) and, more- 

 over they are stationary and fill the whole field of vision. 



131. Other phenomena which are probably allied to, but can bear 

 no very close comparison with the one in question may be mentioned as 

 follows : — 



Vierordt's phenomenon of tortuous and entwined " streamings," 

 which are visible with intermittent light, and also after the blood has 

 been driven to the head through stooping (perhaps similar to the stream- 

 ing off of the bright points in the phenomenon as first observed (par. 

 3 et seq.). Again. Steinbnch and Pnrkinje " have observed, Tvath slight 

 pressure on the eye, rows of flowing spherules. Pnrkinje observed also, 

 to right and left of a whitish circle, two vertical light lines in which 

 the spherules moved, on the right, downwards; on the left, upwards. 



132. Among phenomena which are probably more closely related 

 may be mentioned the following : — • 



Helmholtz noticed occasionally a flickering, as from small moving 

 bodies when looking at a wall covered with rough lime and illuminated 



1 "Phys. Optik." § 2.5, 2nd Edition. 



= " Eine bisher noch nicht bekaunte subjective Gesichts erscheinung. " Graefes 

 Archiv.. Vol. 30 (.3). page 329. 



^ " Beobachtungen u. Versuche zur Physiologie de Sinne." Berlin, 1823-25. 



