In old astrology, a planet was said to be in its “exaltation” when it was in that sign of the zodiac in which it was supposed to exercise its strongest influence. Thus the exaltation of Venus is in Pisces, and her
“dejection” in Virgo.
And thus, God wot, Mercry' is desolate' In Pisces, wher Venus' is exaltate'.
In chemistry, the refining or subtilising of bodies, or of their qualities, virtues, or strength.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894