38 Proceedings of the Royal Society 
appears as a circular luminous field; and finally, that I find these 
alterations of area, so easily seen, may he taken as indications of the 
movements of the iris. 
The third method is equally simple. The lachrymal fluid on the 
surface of the cornea affects the image of any light source, such as 
a lamp or star, and by refraction causes the appearance of rays to 
emanate therefrom. 
It is obvious that the length of these rays must he regulated by 
the iris, this organ being nearer to the retina, hence when the pupil 
contracts the rays ought to shorten, and when the pupil expands 
the rays ought to lengthen out. Such I find to be the case. 
Sect. III. The First or Reflection Method. — The following is the 
simplest form of the experiment I have been able to devise. Bur- 
nish the head of an ordinary brass pin, and place the pin up to head 
in a black hat. Now, with one eye shut and your back to the light, 
bring this pin-head near to the other eye so that the light may he 
reflected into it from the convex surface of the pin-head. 
One sees a circular luminous field, with projecting hairs at the 
bottom which belong to the top eyelid.* Globules of the lachrymal 
fluid also appear at each wink. 
Expt. 1. Shade the light from the observing eye for a few seconds, 
then let the light fall on it again. Notice the alteration in area of 
the field of view. The field contracts, then expands slightly, and 
oscillates until the iris is adjusted for the amount of light falling 
into the eye. 
Expt. 2. Observe the pin-head with the right eye for some 
moments, the left eye being closed. Open the left eye. The iris 
of the right eye is seen to move markedly, the pupil contracting. 
Here the iris of the right eye is moved by the light entering the left 
one. 
Expt. 3. With everything as in Expt. 2, have both eyes closed 
and only open the right or observing eye. There is contraction of 
the pupil, hut apparently no more marked than in Expt. 2. 
* A simple method is here suggested for demonstrating to one’s self the in- 
verting action of the crystalline lens. With everything as here described, take 
a needle and bring it across the field of view close to the eyelids. If it move 
downwards , it appears to move upwards ; if it be moved upwards, it appears to 
come downwards. 
