( '73 ) 
different note, yet the real number of notes 
is no more than feven, which are called by 
the firft feven letters of the alphabet. If 
you begin with A, and ftrike feven notes in 
fucceflion upwards or downwards, you will, 
either way, come again to A : they are not 
indeed the fame notes as that with which 
you began j but they are octaves to it, vi- 
brating, the one in half, the other in double 
the time. > i: o 
Thefe feven notes are thofe of a peal of 
feven bells : when there are eight, the fmalleft 
bell is an octave to the largeft. But if mu- 
fical inftruments contained no other than 
thefe feven notes and their odtaves, they 
would produce no better melody than that 
wretched jumble of founds called ringing 
changes; or, at beft, but a very fimple tune: 
therefore to render thefe inftruments more 
comprehenfive, intermediate notes, called 
femitones, were introduced, each half a tone 
higher than the note below it, and confe- 
quently half a tone lower than the note 
above. Thefe are the fhort white keys on 
the harpfichord. In confequence of this 
arrangement, the whole octave confifts of 
1 2 femitones, for they are each half a tone 
higher or lower than the next. 
But, 
