Optical Illusion of the Week!

Day's sine illusion is best appreciated interactively.  Here is a sine wave (or if you prefer, a curving path) formed of vertical lines. Compare the length of the lines in the drawing. Would you believe all the lines are precisely the same length? They are, as you can verify by direct measurement, or by clicking on the image, in which case you will be taken to an interactive version where you can smooth out the wave. Another interactive version is here. And here is Michael Bach's recent (March, 2007) version.

A bonus. Note that the colored circles appear to be staggered up or down slightly. In fact, they are all on the same line.