[turnbull] a subjective PHENOMENON OF VISION 3S 



lead one to suppose that the phenomena described by him and the 

 writer are closely allied, whereas other passages would lead one to 

 think that if both see the pigment granules, they act in the different 

 eyes in a very different manner. Probably the most concise description 

 of the phases he sees, that correspond at all nearly to the pbases seen 

 by the writer is given in the following paragraph : — 



'■ One sees exceedingly fine, more or less bright lighting points 

 which are also in continual motion. Some of these finest lighten up 

 exceedingly bright, others, on the contrary, lighten up weaker, and 

 in part only with the same pale blue colour as the above mentioned 

 spot. Some of these points are indeed quite dark and hardly dis- 

 tinguish al)le. The motion of these points is not, as in the case with 

 the circulation, a forward locomotion; it is much more a toothlike to 

 and fro trembling in short, straight lines; an emergence and disappear- 

 ance; occasionally also a short stand-still. 



142. The image seen by the writer is so small, and of such a 

 regular nebulous form and constant motion, that in many respects it 

 seems incomparable with the phenomenon as above described. The 

 pale l)lue colour of some single points lighting up " exceedingly bright," 

 weaker points and dark ones, disappearances and standstills, accord but 

 poorly with the phenomenon as observed by the writer, and yet in the 

 to and fro motion there is a similarity that points to both phenomena 

 being due to the same cause. Perhaps the writer sees the central 

 part, of Zehender's phenomenon, and only the central part, but sees 

 it more clearly than Zehender, for, instead of a " to and fro trembling," 

 the motion has a distinct oscillatory character in my eyes — there is 

 occasionally a very pale Ijlue background to the image seen ])y me, 

 which may correspond to Zehender's points, which lighten up with a 

 pale blue colour. 



143. A review of the subjective phenomena of vision, in which 

 the circulation of iDlood in the capillar)^ vessels of one's own eye is 

 thought to be seen, would here be out of place, as in these phenomena 

 rows of spherules are seen moving, to be sure, but always over the 

 same paths and in the same direction. 



144. The quoting of further references of a similar nature to 

 those above is unnecessary. Suffice to say, that in all the literature to 

 which the writer has had access, no mention has been made of either 

 a hexagonal or a nebular image having a regular oscillatory motion ; 

 consequently, no mention of the constancy (under certain conditions) 

 of this motion nor mention of the conditions affecting this motion, nor of 

 the changes it undergoes, and not even any attempt to count the oscil- 

 if tions of bright points " having a certain to and fro motion," which 



