USELESSNESS OF AIR AS TRANSMITTING MEDIUM PROVED FROM SIGHT OF OBJECTS AT NIGHT.
3. A strong proof that the forms of sense-objects are not seen merely because the air, on being affected, transmits them by relays from point to point, is that even in darkness the fire, the stars, and their forms may be seen. In this case no one would claim that the forms of the objects, being impressed on the obscure air, are transmitted to the eye; otherwise, there would be no obscurity, as the fire, while transmitting its form, would illuminate. Indeed, in the profound obscurity in which the light of the stars is not seen, the fire of signals and of light-houses may be perceived. Should any one, in opposition to the testimony of his senses, claim that even in this case the fire penetrates the air, he should be answered by having it pointed out to him that in that case human vision should distinguish the smallest objects which are in the air, instead of being limited to the perception of the fire. If then we see what is beyond a dark medium, it would be much better seen without any medium whatever.