as are the two wires on a harpfichord, which 
form each individual note. I fpeak of a 
harpfichord without oftaves. Unifon there- 
fore is the only perfect concord. Other 
chords are more or lefs perfect as their vi- 
brations coincide more or lefs frequently. 
The next chord in degree of Harmony is 
the Oclave, becaufe, as it vibrates in half, or 
in double, the time, the tones coincide at every 
fecond vibration. The Oclave, you remem- 
ber, is the tone of a firing half the length: 
that is, the tone on each fide of the bridge, 
of a firing divided into two equal parts. 
Now, if I remove the bridge, fo as to leave 
three parts of the whole firing on one fide, 
and two on the other, the longefl divifion 
will found a 5th to the whole firing, and if 
they were founded together, there would be 
a perfect coincidence at every third vibra- 
tion : the 5th therefore is the next chord in 
rank. You now move the bridge, fo that 
there fhall be three fourths on one fide; this 
longer part will found a fourth to the whole 
firing, and their vibrations will unite at 
every fourth return. You then move the 
bridge fo as to leave four 5ths on one fide: 
the longefl divifion will found a major third 
to the open firing, and the vibrations of 
M 4 two 
