Take a box about 18 inches long by six deep, and remove the lid and one
side. In the centre set a square of glass at right angles to the bottom,
and parallel with the plane of the ends.
Place a picture which you wish to copy on the left of this upright
glass, and a sheet of paper on the right.
On holding the head on the left of the glass, and looking into it
downwards, the reflection or spectre of the picture will be seen on the
paper, where the lines may be traced.