it somewhat below.

~The Continuous Mute.~--Do not try to set a temperament without a
continuous mute. Its purpose is to mute all outside (1st and 3d[C])
strings of all the trios included in the temperament so that none but
the middle strings sound when struck by the hammers. The advantage of
this can be seen at once. The tuner tunes only the middle strings in
setting the temperament and thereby avoids the confusion of hearing
more than two strings at once. The continuous mute is then removed and
the outside strings tuned to the middle. Without the continuous mute,
he would be obliged to tune all three of the strings of the unison
before he could tune another interval by it, and it would not be so
safe to tune by as a single string, as there might be a slight
discrepancy in the unison giving rise to waves which would confuse the
ear. The tuner should hear but two strings at once while setting a
temperament; the one he is tuning by and the one he is tuning. A
continuous mute is a strip of muting felt of the proper thickness to
be pushed in between the trios of strings. Simply lay it across a
portion of the strings and with a screwdriver push it in between the
trios just above where the hammers strike. In the square piano, which
has but two strings to a key, the continuous mute cannot be used and
you will be obliged to tune both strings in unison before leaving to
tune another interval. This is one of the reasons why the square piano
does not, as a rule, admit of as fine tuning as the upright.

[C] The three strings composing the trio or unison are numbered 1st,
2d or middle, and 3d, from left to right.

It is presumed that you are now familiar with the succession of tones
and intervals used in setting the temperament. Fix these things in