108 Contributions to the Physiology of Vision. 



was similar to fig. 15 : the oblique and almost perpendicular 

 direction of the arch was of course gradually changed into the 

 former horizontal one, when the wire was carried back to its 

 former place. During a quick repetition of shocks, there ap- 

 peared, in the light places above and below the arch, parallel 

 curved lines, alternately light and dark, which intersected each 

 other and formed squares, but of much larger size than were 

 observed in any of the former experiments : these squares were 

 also, and still more distinctly, seen when the lower conductor 

 was brought into contact with that near the eye. When, 

 during the galvanic experiment, the eye was pressed, the 

 luminous rhombus, &c., appeared, and nothing could be seen 

 of the galvanic figure ; when strong pressure was exerted, figs. 

 21 and 22 were perceived, and on every shock the ramifications 

 proceeded from the dark centre with a most beautiful violet- 

 coloured light. 



IV. Nebulous stria. If the eyes are well protected against 

 external light, and the observer fixes his attention to the dark- 

 ness before them, nebulous figures and glares are soon seen 

 to arise, which at first are extremely vague and almost form- 

 less, but gradually acquire a more distinct and perceptible 

 shape ; they consist of luminous streaks with dark intervals, 

 and move in a centripetal, transverse, or circular direction 

 (figs. 16, 17, 18). Their motion is rather slow, and, in Dr. 

 Purkinje's eye, about eight seconds elapsed between the rising 

 and disappearing of one of the transverse streaks. When the 

 experiment was continued for a few minutes, Dr. Purkinje 

 distinguished the following figures : 



1. A feeble glare in the middle, surrounded by dark con- 

 centric rings, and the intervals between them filled with a 

 faint light, which gradually loses itself in the darkness of the 

 rings ; the whole figure is in continual centripetal motion, the 

 gleam of light in the middle gradually fades and makes room 

 for the shade of the next ring, which, having now become a 

 dark spot, also disappears, &c. 



2. At other times the light comes from above as a large 

 horizontal luminous streak (fig. 17) ; it slowly moves down- 



