In the _New Grove Dictionary_ will be found an extensive
article "Pianoforte," and a shorter note, "Square pianoforte,"
with a reference back to the larger article; which has (as
usual) an excellent bibliography. I don't know that "Grove" is
available online - but Hey, take a nostalgic trip back in time,
to that quaint world of print and paper, those long-ago days of
yesteryear. There is a certain sensory satisfaction to the look
and feel of an actual _book_; the weight, and heft, the texture,
the aroma. Many have forgotten the skills needed to operate
one, but much of it is intuitive.