flat-A flat-C or C-E flat-A flat or A flat-C-E flat). Then try it as
fifth in the chord of F (C-F-A or A-C-F or F-A-C). Take G likewise and
try it as fundamental in the chord of G in its three positions, then
try it as a third in the chord of E flat, then as fifth in the chord
of C. In like manner try every tone in this way, and if there is a
falsely tempered interval in the scale you will be sure to find it.

You now understand that the correctness of your temperament depends
entirely upon your ability to judge the degree of flatness of your
fifths; provided, of course, that the strings stand as tuned. We have
told you something about this, but you may not be able at once to
judge with sufficient accuracy to insure a good temperament. Now, we
have said, let the fifths beat a little more slowly than once a
second; but the question crops up, How am I to judge of a second of
time? The fact is that a second of time is quickly learned and more
easily estimated, perhaps, than any other interval of time; however,
we describe here a little device which will accustom one to estimate
it very accurately in a short time. The pendulum oscillates by an
invariable law which says that a pendulum of a certain length will
vibrate always in a corresponding period of time, whether it swings
through a short arc or a long one. A pendulum thirty-nine and a half
inches long will vibrate seconds by a single swing; one nine and
seven-eighths inches long will vibrate seconds at the double swing,
or the to-and-fro swing. You can easily make one by tying any little
heavy article to a string of either of these lengths. Measure from the
center of such heavy article to the point of contact of the string at
the top with some stationary object. This is a sure guide. Set the
pendulum swinging and count the vibrations and you will soon become
quite infallible. Having acquired the ability to judge a second of
time you can go to work with more confidence.