8 H. W. Poole on Perfect Harmony, etc. 
by pedals, one for each key, which put the organ in tune for its — 
own scales. It could be played without the player knowing what 
sounds he used—he only needed to keep the organ in the right 
key. Gen. Thompson justly remarks that his system would 
have merits over ours, in compelling a musician to know what ~ 
he is doing. But in the dark days of enharmonic science it 
may be excusable not to demand too much of the organists. 
. There are great difficulties which present themselves in 
admitting to a key-board the multitude of sounds required if — 
several transpositions or signatures are to be played in. If the 
five series of sounds already described, § 12, are carried into the 
keys from nine flats to nine sharps—nineteen signatures—just — 
one hundred notes to the octave are required! But an octave 
is limited in width by the span of the fingers. Six and a half — 
inches is about the convenient average measure, and this is 
adopted by organ and piano-forte makers. If the notes we 
want are divided equally into this space each will get the hund- — 
redth part of it, or sixty-five thousandths of an inch. The pins ~ 
of a barrel organ might play upon them, but with human fin- 
gers it is hardly possible. 
17. But there is a fortunate circumstance in the relation of 
the sounds which comes to our aid. All are not wanted at the 
same time; when we are near the key of nine sharps there is — 
no possibility of our requiring the notes of nine flats. These 
we may arrange therefore at a distance front or back, and place ~ 
near by the i 
related notes which may be required in connection 
with those already in use. 
18. At least seven finger-keys should be in convenient rela- 
