THE CAMERA OBSCURA AND CAMERA LUCIDA.
The construction of the camera obscura is founded
on the fact that the rays of light, when collected
into a point either by being passed through a small
hole or a converging lens, form an image of the objects
from which they proceed at the point of meeting.
This may be readily tried by piercing the shutter of a
room with a small hole, and holding a piece of paper
within a short distance of it. It will be noticed that
the smaller the hole the more distant will be the
image formed. The first person who observed this fact
was John Baptist Porta, an Italian philosopher who
lived in the latter part of the seventeenth century. He
noticed that when a screen was placed opposite a small
hole in the shutter of his room, the objects outside were
depicted on it in a reversed position with moderate distinctness;
but that when a biconvex lens was placed
over the hole, the picture was rendered much more
distinct. This was the first attempt at the formation of
the camera obscura, an instrument that has since bestowed
such incalculable benefits on humanity.
The shape of the images so formed is independent of the shape of the opening, which, as long as it is sufficiently small, may be square, oval, or triangular. This may be easily seen when the sun shines through the intervals between the leaves of a shady avenue or bower
