[Illustration]
Take a piece of pasteboard, about five inches square, roll it into a
tube with one end just large enough to fit round the eye, and the other
end rather smaller. Hold the tube between the thumb and finger of the
right hand; put the large end close against the right eye, and with the
left hand hold a book against the side of the tube. Be sure and keep
both eyes open, and there will appear to be a hole through the book, and
objects, seem as if through the hole instead of through the tube. The
right eye sees through the tube, and the left eye sees the book, and the
two appearances are so confounded together that they cannot be
separated. The left hand can be held against the tube instead of a book,
and the hole will seem to be as if through the hand.