in a creature of vast size - one say, of 1,000 miles long - as in that case, instead of the object being seen all at once, the unity and wholeness of it is lost to the beholder.
The context of this quote is that Aristotle is discussing beauty. Aristotle says that a crucial aspect of beauty is that it is a harmony of parts that contribute to a unity or wholeness of an object. In Poetics he is talking about plays and stories. He says that we cannot perceive extremely small objects to be beautiful or not because we cannot see all the parts; and we cannot perceive extremely large object as being beautiful or not because we cannot see the whole. So basically, a play or story shouldn't be too long or too short.
When I read this though, I got a picture in my head of the satellite images of Earth, and what an absolutely gorgeous picture it is. How lucky we are to be able to get that perspective and to see the whole of the earth, when Aristotle never got to.
