The first mention of this I have seen is in Aristotles *De Anima*: >419a15 For Democritus did not speak rightly, thinking that if the intervening space were to become a void, then even if an ant were in the sky it would be seen accurately; for this is impossible. >For seeing takes place when that which can perceive is affected by something. Now it is impossible for it to be affected by the actual colour which is seen; it remains for it to be affected by that which is intervening. > But if it were to become a void, not only should we not see accurately, but we would see nothing at all. A goes into this in more detail in his *Physics*. It's this notion thats later codified into the principle of *locality*, of which there are a few variants.