14 ROYAL SOCIETY OF CANADA 



eyes and despite all efforts to retain them in the visual field, they invari- 

 ably disappeared in course of a second or two leaving only the "proper 

 lighf of the retina behind. 



4. The image which oscillated could hardly be called distinct and yet 

 it seemed to consist of yellowish or whitish lines grouped together, in the 

 centre of the image, in the manner of the lines in b fig, 1, the border of 

 the image was extremely indistinct and blended insensibly in'to the dark 

 background. On account of the rapidity of the oscillations it was not 

 easy to coimt the number of hexagons making up the more distinct) or 

 central portion of the image or to estimate the angle which the image 

 subtended in the visual field. It is interesting here to note the similar- 

 ity between this image and illustrations of the crystalline lens cells.^ 



6. For perhaps 15 years the phenomenon just described appeared 

 occasionally, after retiring, but no attempt was made to study it. Some 

 thing over a year ago (now April, 1904 — 9 years ago), however, after 

 repeated efforts to retain the image in the visual field, the writer suc- 

 ceeded, by practice, in observing what is, apparently, a modification of 

 the original image. 



7. The more recently observed image seems to be nothing more than 

 a group of indistinct light points — ^a kind of nehuloiis image — which 

 oscillates as did the first and has an indistinct circular or elliptical 

 border blending insensibly into the background. 



8. This image when seen in darkness seems to be something more 

 than the " proper light " of the retina. With most people the " proper 

 light " consists of light points or " light-dust " in a confusing 

 state of motion, but in the writer's eyes the motion of the nebu- 

 lous image can be followed — perhaps only on account of the introduc- 

 tor}' lessons given by the image as first observed. Every instant or two 

 some points instead of oscillating regularly seem to start from the image, 

 but the nebulous image, as a whole, keeps on oscillating regularly so that 

 the vibrations may be counted. 



9. Ever since seeing this image the former image has been seen 

 occasionally. 



10. The plane of oscillation of the image - seems to be more or 

 less vertical, but it does not remain const/a.nt and there seems to be a shif- 

 ting of the plane to 30 or 40 degrees on either side of the vertical. 



^ Quain. " Elements of Anatomy," 1895, Vol. Ill, Part III, p. 64, Fig. 75B. 

 This book is heartily recommended to the physicist, interested in this article, 

 who wishes to find a complete and exceedingly good anatomical description of 

 the eye. 



" By " the image " will hereafter be always meant the nebulous image, which 

 is the usual one at present observed. 



