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W. L. Stevens—Organ-Pipe Sonometer. 479 
Arr. LVI.—An Organ-Pipe Sonometer ; by W. LECONTE 
EVENS.* 
WHILE using the sonometer in illustrating the laws of vibra- 
tion of stretched cords and the nature of musical scales, it has 
been found desirable to have an instrument on which division- 
marks were properly arranged to furnish the operator the means 
of contrasting the scale of equal temperament with the true 
natural scale, and thus showing to some extent the error of the 
ordinary keyed instruments. In demonstrating the laws of vi- 
bration of columns of air, moreover, it is not always easy to 
obtain the successive notes of the harmonic series from a single 
pipe. If the fundamental is pure and strong, either the upper 
harmonics are unattainable or several are attained at the same 
moment, and the untrained ear fails to single out the one to 
which attention is invited. If a single standard of pitch be 
kept at hand for comparison, the auditor must be practiced in 
estimating musical intervals; hence a tuning fork alone is not 
sufficient for most persons. It occurred to me that the union 
of sonometer with organ pipe in a single instrument would be 
attended with some advantages, particularly in connection with 
the exhibition of Bernoulli’s laws. The following device has 
been found very satisfactory. : 
The resonance-box consists of a double organ pipe of spruce, 
which is rested horizontally on the lecture table. e two em- 
may be thrust, by means of its handle, half way into one of 
the pair, converting it at will into a stopped pipe whose funda- 
mental is the same as that of the open pipe of double its 
length, 
The upper wall consists of a single plate of pe 5™™ thick, 
that forms the sound-board of the sonometer. Firmly fixed at 
each end is a bloek of hard wood (é, 6’) into which pee pins 
s 
are driven for the attachment of three steel wires which pass 
over the fixed bridges (¢, ¢’). The latter are exactly 1® apart, in 
contact with the ends of a strip of wood divided at each edge 
into millimeters, and occupying the middle of the sound-board. 
This strip not only serves as a guide for the movable bridges 
- _ * Presented before the New York Academy of Sciences, May Ist, 1882. 
