242 Mr. Shelford Bidwell. 



fifteen. In Helrnholtz's 'Physiological Optics,' drawings are given 

 illustrative of the phenomena exhibited by a luminous point when the 

 conjugate focus is situated a little in front of or a little behind the 

 retina. A narrow luminous line such as that formed when a spectro- 

 scope slit is held before a flame or other bright background may 

 become similarly multiplied. These and other allied phenomena are 

 believed to arise from the suture-like radial lines, six or more in 

 number, which occur upon the two surfaces of the crystalline lens. 



It is also known that as the result of disease or malformation of the 

 eye, the patient may habitually see several images of single objects.. 

 But in the course of a careful search among physical and physiological 

 publications, in which Dr. Dawson Turner, of Edinburgh, has most 

 kindly assisted me, I have been unable to find any reference to certain 

 curious phenomena of vision which attracted my notice in the year 

 1897, and which form the subject of the present communication. It 

 appears that under suitable conditions a normal healthy eye can see 

 hundreds of independent images of a single point, an effect which 

 probably results from the cellular structure of the lenses and the mem- 

 branes associated with them. 



In the earlier observations, the object consisted of a small bright 

 disc. Several different discs were employed, their diameters ranging 

 from 0*5 mm. to 8 mm., and other details were also varied, but (when 

 the circumstances were suitably modified) the results were in all cases 

 of the same nature. It will be convenient to describe the procedure 

 actually carried out in a particular experiment ; but, except as furnish- 

 ing a rough guide for the repetition of the experiment, no special 

 importance must be attached to the distances mentioned ; they vary 

 greatly for different individuals, and from time to time even for the 

 same eye. 



. The condenser of a lantern was covered with two sheets of glass, the 

 one ground and the other deep red. In front of these was placed a 

 brass plate, in the middle of which was drilled a hole -f^ inch (2 mm.) 

 in diameter. Inside the lantern was an incandescent electric lamp of 

 25-candle power. The observer, standing with his left eye at a 

 distance of about 2 feet from the hole in the plate, first covered the 

 hole with a concave lens of 11 inches (28 cm.) focal length, held in his 

 hand, and then slowly moved the lens towards his eye. When the 

 lens was some four or five inches away from the hole, the outline of the 

 little bright disc began to appear multiple ; there seemed, in fact, to be 

 a number of little discs almost, but not quite exactly, superposed. As 

 the lens approached the eye, the images became gradually more and 

 more widely dispersed, and when the eye was reached, they had 

 become completely separated. There now appeared to be seven bright 

 discs a central one surrounded by six others, their arrangement being 

 fairly symmetrical ; these were backed by an irregular luminous haze 



