206 On Refraction. 
ceived a beautiful reflected image of the letter T. I now placed 
the bull’s eve immediately in front, and then perceived this 
image to be ‘considerably magnified i in-all its dimensions and sur- 
rounded with colours: he éaid he saw exactly similar to the re- 
flection on his cornea. | would now beg leave to ask, Did this 
gentleman perceive the letter T by a reflected or refracted image? 
On removing the bull’s eye to yet a greater distance from the 
pupil, I distinctly perceived two reflected i images, the one erect, 
the other inverted. Again I would ask, Is it possible by refrac: 
tion to produce in the focus of a lens both an erect and an inverted 
image at one and the same time? That we see by means of re- 
flected and not refracted images, is therefore evident. This expe- 
riment is easily repeated with the glass globe instead of an as- 
sistant’s eye. On a sheet of white paper write the letter T, and 
hold over it the bull’s eye : when close to the paper, the letter i is 
considerably magnified s on bringing it somewhat nearer to the 
eye, two iwverted and coloured images are perceived to float on 
the posterior surface. On now giving a circular motion to the 
lens, these reflected images, in revolving round the erect one, 
become inverted or erect; when at the top and bottom they are 
inverted; when at the sides erect; for which phenomenon I am 
as yet unable to account. At yet a greater distance these two 
images form a circular appearance, margined on the inside by 
orange rays, and at length coalescing form one inverted image, 
which floats around the erect image with each revolution, with- 
out charge. When we look at an object, its picture is painted 
on the cornea, and thence converges to the sensorium in the same 
manner as with the other senses. By placing a concave lens be- 
fore the eye, this reflected image is diminished; by placing a 
convex one it is magnified. A short-sighted person sees objects 
large and confused when at a distance ; a concave lens obviates 
this defect, by painting a small and well-defined imaye close to the 
eyes; for a near-sighted person can read small print when near 
without glasses. In old age the humours become decayed and 
turbid, and the corneal image is not sufficiently strong to make 
an impression on the retina, the principal nerve of the eye. 
Therefore a convex lens is necessary for the purpose of forming a 
magnified image closer to the eye, and also for the purpose of 
illuminating that image and throwing a greater quantity of light 
into the eye. Any person may make himself near-sighted either 
by constantly examining near and small objects, or by the wear- 
Ing concave glasses; for by these means the eye becomes accus- 
tomed to the strong stimulus of rays from near objects, or from 
the images near the eyes. In a similar manner, a person may 
make himself deaf, by constantly accustoming the ear to intense 
noises, such as the roar of cannon, &c, + 
Ir. 
