Join two square parallel ends by a third piece, half an inch broad and
an inch and a half long, using a piece of cardboard doubled up, with
that interval between, as the simplest material. In the middle of one
end make a round hole, a little more than one-twelfth of an inch wide,
and in the centre of it fix the head of a pin or point of a needle.
Directly opposite, in the other side, make a large pinhole. If the
latter is held to a strong light, and the eye is applied to the other
hole, the head of the pin will be seen, not only greatly magnified, but
turned upside down.