Dave's question has already been answered, and the consensus has been "wide
side up", but why?
Is it simply eye pleasing proportions, a standard we've become accustomed
to, or something else?
I found a reference that stated "Together, the chair rail, the wainscoting,
and the base molding parallel the pedestal of classical design, where the
chair rail is the cornice, with the fancy embelishment acting as the frieze,
the wide board is the dado, and the base molding is the plinth" Ref:
This is borne out clearly by a diagram at
<http://www.probertencyclopaedia.com/T2.HTM where, if you look at the
pedestal of the column, it is easy to imagine it as the portion of the wall
under discussion. The chair rail (cornice) is clearly shown "wide-side up",
the same as the cornice in the entablature or the abacus in the column's
capital. Study of the classical column will answer a lot of questions, I
found this particular diagram very helpful to understand how the various
interior elements come together as a metaphor for the column.
What I did not find was a scale that would help with sizing the various
components to a ratio that suits the architecture of a room so it looked
balanced, though it must be out there somewhere - anyone?