William Peterson's quote from Williamson makes sense to me.
When I have an extensive bibliography to go through in the stacks
I sort it in order by call number and then proceed to search
along the shelves in ascending order -- by those call numbers --
so tilting my head "to the right" makes a lot of sense, as
"right" is the direction in which my call number list is heading
me, while a tilt to the "left" would be a recipe for dizziness
and a stiff neck...
I expect the same is true for book lists alphabetized by author
or by title -- they would be searched, in library stacks or on
bookshop shelves, in ascending order i.e. "left to right", and
for this heads would bend most easily rightwards...
What Peterson quoted Williamson as saying was:
> "Those who favour the upwards style maintain that the head is
> more easily turned to the left for vertical reading than to
> the right, and that a whole row of upwards titles on a shelf
> can be read in the natural direction, from left to right.
> Most of the other arguments for this style arise from strong
> personal preferences or from the custom of leading
> publishers.
>
> "The advantages of the downwards style are less abstruse. If
> the lettering travels down the spine, the title can be read
> when the book is lying flat and with the front of the book
> uppermost."
Jack Kessler, kessler@well.sf.ca.us