There were many smaller organs, as, for instance, the one in the
monastery of Ramsey, which had copper pipes. Pictures of others
from the twelfth century show that even where there were only
ten pipes, the organ had two manuals, needed two players, and at
least four men for the bellows. The great exertion required to
play these instruments led to the invention of what is called
"mixtures." From the moment fifths and fourths were considered
to sound better together than the simple notes, the pipes were
so arranged that the player did not need to press two of the
ponderous organ keys for this combination of sounds. One key
was made to open the valves of the two sets of pipes, so that
each key, instead of sounding one note, would, at will, sound
the open fifth, fourth, or octave. With the addition of the
third, thus constituting a perfect major triad, this barbarous
habit has come down to our present day almost unchanged, for by
using what is called the "mixture stop" of our modern organs,
each key of the manual gives not only the original note,
but also its perfect major triad, several octaves higher.

Originally the organ was used only to give the right intonation
for the chanting of the priests. From the twelfth century, small
portable organs of limited compass were much used; although the
tone of these instruments was necessarily slight, and, owing to
the shortness of the pipes, high in pitch, the principle of the
mechanism was similar to that of the larger instruments. They
were hung by means of a strap passed over the shoulders;
one hand pressed the keys in front of the pipes (which were
arranged perpendicularly), and the other hand operated the
small bellows behind the pipes. These small instruments rarely
had more than eight pipes, consequently they possessed only
the compass of an octave. With slight variations, they were
quite universally used up to the seventeenth century. Organ
pedals were invented in Germany about 1325. Bernhard, organist
of St. Mark's, Venice (1445-1459), has been credited with the
invention of organ pedals, but it is probable that he merely
introduced them into Italy.

As the Greek modes formed the basis for the musical system of
the church, so the Greek monochord is the type from which the
monks evolved what they called the clavichord. The monochord
has a movable bridge, therefore some time is lost in adjusting
it in order to get the different tones. To obviate this
inconvenience, a n