erve, for
instance, for D sharp and for E flat, whereas the two notes are in
reality not identical.[1] To secure correct tuning and tone intervals
throughout, forty-eight keys per octave are required, instead of the
twelve now made to suffice.

In what is called the _equal temperament_ system the attempt is made to
divide the octave into twelve equal parts or semi-tones, thus rendering
all keys alike. To do this it is necessary to slightly flatten all the
fifths and sharpen the major thirds. The difference from just
intonation is about one-fiftieth of a semi-tone. Although recommended
and used by J. S. Bach, equal temperament was not introduced into
English organs until 1852.

Much has been lost by adopting equal temperament, but more has been
gained. To a sensitive ear, the sharp thirds and fourths, the flat
fifths and other discordant intervals of our modern keyed instrument,
are a constant source of pain; but the average organist has become so
accustomed to the defect that he actually fails to notice it!

The change to equal temperament has on the other hand greatly increased
the scope of the organ and has rendered possible the performance of all
compositions and transcriptions regardless of key or modulation.

The tuning of an organ is seriously affected by the temperature of the
surrounding air. Increased heat causes the air in the open pipes to
expand and sound sharp contrasted with the stopped pipes through which
the air cannot so freely circulate. The reeds are affected
differently, the expansion of their tongues by heat causing them to
flatten sufficiently to counteract the sharpening named above. Hence
the importance of an equable temperature and the free circulation of
air through swell-boxes, as described on page 59, _ante_.

NEW METHOD OF REED TUNING.

Organ reed pipes, especially those of more delicate tone, fail to stand
well in tune, especially when the tuner is in a hurry or when he does
not know enough of his business to take the spring out of the reed wire
after the note has been brought into tune.

Few persons fully understand the reason why reeds fail to stand in tune
as they ought to.

[Illustration: Figs. 31-35. New Method of Tuning Reeds]

Figures 31, 32, and 33 will serve to make clear the chief cause for
reeds going out of tune. Figure 31 may be taken to represent a reed
block, eschallot, tongue and tuning wire at rest.

In this case the tuning wire will be pressing firm