This word is derived from two Greek words, one of which signifies
_wonder_, and the other _to turn_. It is a very pretty philosophical
toy, and is founded upon the principle in optics that an impression
made upon the retina of the eye lasts for a short interval after the
object which produced it has been withdrawn. The impression which the
mind receives lasts for about the eighth part of a second, as may
be easily shown by whirling round a lighted stick, which if made to
complete the circle within that period, will exhibit not a fiery point,
but a fiery circle in the air.