Oldest Reference to Astronomical Seeing I'm writing a paper on astronomical seeing. Sir Isaac Newton identified both the phenomenon and origin of astronomical seeing in his Opticks. He writes:

If the Theory of making Telescopes could at
length be fully brought into Practice, yet there would
be certain Bounds beyond which Telescopes could
not perform. For the Air through which we look
upon the Stars, is in a perpetual Tremor; as may be
seen by the tremulous Motion of Shadows cast from
high Towers, and by the twinkling of the fix'd Stars.

is anyone aware of any older reference from Gilbert, Galileo, Harvey, Ptolemy, Copernicus or Kepler?
Robert Hooke's Micrographia from 1664 has a detailed discussion of "seeing"

The table [of contents], which is at the end of the book, explains that pages 230-232 discuss:


  that the Air near the Earth is composed of parts of differing density...this property produces the effects of waving and dancing of Bodies; and of the twinkling of the Stars