the Well-Tempered Clavier

the superimposition of musical scales to facilitate
the movement from one scale to another upon a
single instrument without having to each time
tune that instrument is what is meant by
temperament, this appears to have been a
personal adjustment, though of course informed,  
according to each instrumentalist
you’ll note they do that still at the beginning of
any concert, to the tuning dictates of usually the
first violin, who often takes a bow to the applause
of the audience, who mistake him, I’m sure, for
the conductor then, why else so honour that first,
but not especially otherwise eminent, short string 
Bach formalized the process, gave it breadth and
majesty, and ultimately longevity, by composing
his Well-Tempered Clavier, a piece for adjusted
harpsichord originally, which he tuned indeed
himself, and that we hear nowadays most often
on the harpsichord’s more versatile descendant,
the piano
the scales we now listen to in Western music are
Bach’s tempered scales, we would find it difficult
to return to the precise, mathematically accurate 
ones, the most pure, our already skewed tonal
consensus suggests an already altered view of 
the universe not unlike the reimagined orbits of
the earth and sun at the time of Copernicus and
Galileo, all is still essentially exploratory, nothing
but mathematics is stable, we are precariously
balanced in an insubstantiated world, all no surer
ever than illusion
Scott Ross is exemplary 
is no better version, I think, than Glenn Gould‘s 
they establish here faithfully and unequivocally
our musical alphabet
psst: here is a version with moving pictures very
         much worth your while