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 your mind and the system is easy to understand and remember.  Keep within the bounds of the two octaves laid out in Lesson X. Tune all fifths upward; that is, tune all fifths by their fundamentals.  For example, starting on 1C, use it as fundamental, and by it, tune its fifth, which is G; then, having G tuned, use it as fundamental, and by it tune its fifth, which is D, and so on through.  After tuning a fifth, always tune its octave either above or below, whichever way it lies within the bounds of the two octaves.  After going through one or two experiments in setting temperament you will see the simplicity of this system and will, perhaps, not be obliged to refer to the diagram any more.

For various reasons, it is better to try your experiments on an upright piano, and the better the piano, the more satisfactory will be the result of the experiment.  You should have no hesitancy or timidity in taking hold of a good piano, as you cannot damage it if you use good judgment, follow instructions, and work carefully.  The first caution is, be very careful that you draw a string but slightly sharper than it is to be left.  Rest the heel of the hand against some stationary part of the piano and pull very slowly, and in a direct right angle with the tuning pin so as to avoid any tendency to bend or spring the pin.  We would advise now that you find an upright piano that is badly out of tune, if you have none of your own, and proceed to set a temperament.