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The apparatus consists of a base board on which are 
planted the two reed boxes A and B. The box A is placed 
horizontally in such a manner as to be capable of slight 
rotation in the horizontal plane, and also of adjustment in 
height, by means of the support to which it is attached 
being provided with a slot and set screw. The box B is 
permanently attached to the base board in the vertical posi- 
tion. The boxes are so placed that a pencil of light falling 
directly on E would be reflected to B about one inch from 
its top ; they are furnished with clamping screws for the 
attachment of the reeds. The boxes are entirely open on 
the sides facing each other, their margins being covered 
with soft leather on which the reed plates bed, making a 
sufficiently air-tight joint. Wind is supplied through the 
brass tube C which gives off a branch to each box, a stop- 
cock DD' being inserted in each branch. The reeds are 
similar to those used in the construction of harmoniums; 
they are mounted on brass plates which fit the reed boxes. 
The tongue of each reed is furnished, at its free end, with a 
small reflector of microscopic covering-glass (E) silvered by 
Liebig’s process, a piece of cork or pith being inter- 
posed between the tongue and the reflector, so as to free 
the latter from the frame of the reed ; the reeds are then 
tuned in the usual manner. It is not necessary that the 
reeds should be in absolute tune, as, within certain limits, 
their relative vibrations can be adjusted by means of the 
stop-cocks, an advantage of great value, believed to be 
solely possessed by this apparatus. 
The reed in the vertical box gives the fundamental ratio 
of vibrations from which the intervals are built up. Two 
fundamental reeds are used interchangeably, one giving the 
double or eight feet C of musicians, the other, being an octave 
lower in pitch, adds an octave to the intervals obtained 
from the first fundamental : thus, the third with the first 
fundamental becomes the tenth with the sub-fundamental. 
