4 REPORT—1852. 
. any author has treated of the shape of images as affected only by the size of the 
lenses or mirrors by which they are formed. This subject is of fundamental im- 
portance in the new art of Photography, when the images delineated by the solar 
rays are formed by lenses, and sometimes, too, by mirrors of a larger size. 
The images of objects formed upon a plane surface differ from the objects them- 
selves, from many causes which it is unnecessary here to enumerate. The most 
skilful opticians have striven, and to a great extent successfully, to make the most 
perfect lenses for photographic purposes; but the photographer himself has over- 
looked the greatest imperfection to which his art is subject, arising solely from the 
size of the lenses in his camera. 
According to the geometrical principles of perspective, the correct representation 
of any body or object whatever, upon a plane surface, is obtained by drawing lines 
from the point of sight, through every point of the body or object, to that plane. 
As the pupil of the human eye is little more than two-tenths of an inch in diameter, 
we may regard the picture on the retina as a correct representation of external 
objects, in so far, at least, as its correctness depends upon the size of the lens which 
forms the picture. In like manner we may consider the image of objects formed by 
a lens the size of the pupil of the eye as a correct representation of the object. 
Now if in perspective we take a new point of sight two-tenths of an inch distant 
from the first, the perspective representation of the object on a plane will be changed, 
and the magnitude of the change will increase with the distance between the two 
points of sight. In like manner, if we look at an object from two different points, 
which are two-tenths of an inch distant, we shall obtain two views of that object 
equally dissimilar. - 
Following out this principle, let us suppose that a lens four inches square is 
employed to produce upon a plane surface the image of any object, and that the 
size of the pupil of the eye is two-tenths of an inch; then, as there will be several 
hundred areas equal to that of the pupil in the lens, the image given by the lens will 
be a compound image consisting of several hundred perspective views of the object 
taken from several hundred different points of sight, each distant two-tenths of an 
inch from its neighbour, and all those on the margin of the lens distant three inches 
and eight-tenths from those opposite to them. Such a jumble of images cannot, 
under any circumstances, be a true representation of the object. This view of the 
question, as one of perspective, will be more intelligible if we consider the subject 
optically. 
Let LL be either the horizontal or the vertical section of a lens, by means of 
which an image or picture of the object 
Fig. 1, ABCDE is to be taken either on a plane sur- 
face, or suspended in the air, and made visible 
to an eye behind the lens. The solid object 
ABE consists of a cylindrical portion ABDC, 
whose termination AB is a circle, and of a 
conical portion CDE. If we continue the 
lines EC, ED, and CA, DB, they will meet 
the lens in the points c,a,d,b. If we now 
cover all the lens except the central portion 
ab, the image of the object ABE will be 
merely a circle, as shown at ab, fig. 1, because 
not a single ray from the cylindrical surface 
: ABDC, nor from the conical surface CDE, can 
Fig. 2. reach the lens ab. In like manner, if we cover 
all the lens except cd, the image of the ob- 
ay ae "s aa O ject ABE will be, as shown in fig. 2, at cd, 
PD “ its circular termination, and the cylindrical 
~ part of it only being seen, because not a single 
ray from its conical part CDE can fall upon 
the lens cd. But when the whole area LL of the lens is exposed, the whole object 
will be seen suspended in the air, as at LL, fig. 2. 
If the image is received upon a plane surface behind the lens, the cylindrical part’ 
will be represented by a halo or circle of light surrounding the circle ab, and cor- 



