Now this is so arranged that if more than one kind of sensible object is perceivable through a single medium, the possessor of a sense organ homogeneous with that medium has the power of perceiving both kinds of objects (for example, if the sense organ is made of air, and air is a medium both for sound and for colour); and if more than one medium can transmit the same kind of sensible objects, as eg water as well as air can transmit colour, both being transparent, then the possessor of either alone will be able to perceive the kind of objects transmissible through both.