Refraction is greatest when there is a big difference between sea and air temps, and most marked when the observed objects are on the observer's horizon, not his zenith.
As I did stand my watch upon the hill,
I look'd toward Birnam, and anon, methought,
The wood began to move.
Liar and slave!
Let me endure your wrath, if't be not so:
Within this three mile may you see it coming;
I say, a moving grove.
If thou speak'st false,
Upon the next tree shalt thou hang alive,
Till famine cling thee"
Macbeth didn't mix words, did he !
I think, therefore I am. I am, therefore I sail.