1883.] 



Internal Reflexions in the Eye, 



473 



This last formula is derived from (246). I observe that the funda- 

 mental idea by which these integrals are obtained is given by the 



( A + k, cos 6 + . . A r cos rO) (B r cos r<9 + B, +1 cos (r + 1) + . .) = -A r B r . 

 Jo 2 



This method may be much extended. 



II. " Internal Reflexions in the Eye." By H. Frank New all, 

 B.A. Communicated by Dr. M. Foster, Sec. R.S. 

 Received January 18, 1883. 



1. The observation I have to record first came under my notice 

 three or four years ago. Often when working at night by the light 

 of a candle, in a room otherwise dark, my attention was caught by a 

 very faint light some way out of the line of direct vision. This 

 seemed to defy nearer inspection ; for tlie instant I turned my eyes 

 towards it, it was gone, thus showing that there was no objective 

 cause, but that the light was due to some internal reflexion in the 

 eye. Later, however, I found that by keeping the eye fixed and 

 moving the candle, the faint light could be observed at leisure, 

 though, as far as I could then make out, never in the line of direct 

 vision. (See however below, § 32.) 



2. The best conditions soon became apparent, and I have applied 

 two methods in later investigations : (i) One in which, the eye is 

 fixed on a spot on a dark or uniform ground whilst the candle is 

 moved to and fro out of the line of direct vision, (ii) One in which 

 the candle or source of light is kept fixed, whilst the eye follows the 

 regular movement of some point, such as the end of a pencil moved 

 by the hand. 



3. The first of these methods showed that the ghost, as I may call 

 the faint light, moved roughly speaking in a line drawn through the 

 point of clearest vision and the candle, in direction opposed to that of 

 the candle's motion with respect to the point of clearest vision, and 

 with a velocity equal to that of the candle. 



4. The second method showed what is practically the same thing, 

 namely, that the line of movement of the ghost was just as described ;. 

 the direction the same as that of the point of clearest vision over the- 

 field in front j the velocity apparently about double that of the point 

 of regard. 



5. In both methods the ghost merged into the candle close to the 

 point of direct vision, and in other positions seemed about equally 

 removed from that point with the candle. 



equation 



