93 
The horizontal box is furnished with a set of reeds giving 
all the intervals up to the twelfth, including the unison. 
The horizontal reeds are changed for the production of the 
different figures, the fundamental reed being retained. 
It was found, when the wind was allowed to pass directly 
from the bellows to the reed boxes, that the tongues of the 
reeds were simply blown past the openings in the reed 
plates and there sustained, no vibration taking place. To 
obviate this a free space of half an inch was allowed between 
the supply pipe and the reed box, so as to afford a cushion 
of aii* capable of yielding to the elasticity of the tongue. 
The supply pipe is contracted at its termination to about 
one-third the size of the hole in the reed box through which 
the wind enters. 
The apparatus is used as follows : — The base board being 
firmly clamped to a rigid table, one of the fundamental 
reeds is clamped in front of the box B ; another reed, giving 
the desired interval, is similarly clamped to the box A ; an 
elastic tube, about half an inch in diameter, is attached at 
one end to the pipe C, and at the other to an acoustic 
bellows. A fine pencil of light is now thrown on the 
mirror E, which is then adjusted by rotation of the box A 
until the light strikes the mirror of the vertical reed, from 
whence it is reflected on to a screen of tracing paper placed 
a short distance away ; a condenser, interposed between the 
lantern and the mirror E, focuses the spot of light on the 
screen. On the bellows being put in motion the figure 
appears, and can be brought to a perfect stand in any 
phase of development, looped or cusped, by careful manipu- 
lation of one or other of the cocks. The figures are more 
distinctly seen on the side of the screen away from the 
apparatus, the room being in total darkness. It is essential 
to the perfect production of the figures, especially of those 
resulting from the more discordant intervals, that the entire 
apparatus should be as rigid as possible, and free from any 
