In the last the lengths to be compared extend (a) from the right-hand rim of circle 1 to the left-hand rim of circle 2, and (b) from this last to the right-hand rim of circle 3. The same illusion can be got with squares, or even with capital letters as
where the distances between the main vertical lines are to be compared.
Here is an another form of the same illusion
the middle lines being affected by those above and below.
Though these illusions seem like curiosities, and far from every-day experience, they really do enter in some degree into almost every figure that is not perfectly square and simple.
