AMERICAN 
JOURNAL OF SCIENCE AND ARTS, 
[THIRD SERIES] 
Art. XLIX.—On a simple and precise method of measuring the 
wave-lengtis and velocities of sound in Gases ; and on an appli- 
cation of the method in the invention of an Acoustic eler ; 
by Atrrep M. Mayer, Ph.D., Professor of Physics in the 
Stevens Institute of Technology. 
_ The measurement of the wave-length.—Without any consid- 
eration as to the velocity of sound or the number of vibra- 
tions producing a given note, we can accurately measure the 
wave-length of the note by the following simple arrangement 
of apparatus, which is an instrumental simplification of the 
method first used by Zoch (Pogg. Ann., vol. exxviii, p. 497.) 
.. On the acoustic bellows fix an organ pipe, and place opposite 
its mouth a Helmholtz resonator responding to its note. 
of the manometric flame-micrometer* adjust the two flames so 
that their serrations Se coincide when viewed in a cubical 
evolving mirror. Now suppose, for simplicity, that the pipe 
ives 342 complete vibrations in one second ; then, taking the 
Velocity of sound at 842 meters per second (at 15° C.), it will 
Tequire ;}, of a second for an aerial pulse to traverse one 
._* See “On the method of detecting the phases of vibration in the air surround-— 
ing a sounding body; and thereby measuring directly in the vi air the — 
length of its i its wave-surface,” Nov. No. of this 
Journal, In this paper I gave the credit of the suggestion on which I f my 
t I find that it is due to Zoch (Pogg. Ann., vol. exxviii). 
Acoustique without giving credit to the real inventor. — 
Am. Jour. Sct.—Turrp Serms, Vou. IV, No. 24,—Derc., 1872. 
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