We recognize little more of when and the place equipment wheels originated than we do of
the invention of the wheel. Aristotle (c. 384 BC) recorded seeing a train of friction wheels set in motion, that is a series of contiguous wheels with smooth peripheries but without teeth. Ctesibius of Alexandria is said, with the aid of Vitruvius, to have developed a water-clock with gears about a hundred and fifty BC. In this, a primitive rack was once established on a floating drum and meshed with a circular drum so as to rotate it. This is the earliest reference to toothed gearing, but no point out is made of the substances used.
