¢ 
82. A. M. Mayer—Researches in Acoustics. 
prongs of the fork* and of the molecules of air in the resound- 
ing cavityt and in the closed organ-pipe,t we find that each of 
these vibrations follows the same law of reciprocating motion 
as governs the vibrations of a freely-swinging pendulum. But 
other bodies, for instance, the free-reeds of organ-pipes and of 
melodeons,§ vibrate like the pendulum, yet we can decompose 
the vibrations they produce in the air into many separate pen- 
dulum-vibrations, each of which produces in the ear a simple 
sound of a definite pitch; thus, we see that a pendulum- 
vibrating body, when placed in certain relations to the air on 
which it acts, may give rise to highly composite sounds. It is, 
therefore, evident that we cannot always decide as to the simple 
or composite character of a vibration reaching the ear solely 
from the determination of the motion of the body originating 
the sound, but we are obliged to investigate the character of 
the molecular motions of the air near the ear, or of the motion 
of a point on the drum of the ear itself, in order to draw con- 
clusions as to the simple or composite character of the sensation 
which may be produced by any given vibratory motion. Al- 
though we cannot often detect in the ascertained form of an 
aerial vibration all the elementary pendulum-vibrations, and 
thus predetermine the composite sensation connected with it; 
yet, if we find that the aerial vibration is that of a simple pen- 
dulum, we may surely decide that we will receive from it only 
* In my course of lectures on Acoustics, I thus show to my students that the prong 
of a tuning-fork vibrates like a pendul I take two of Lissajous’ reflecting forks, 
giving, say, the major third interval, and with them I obtain on a screen the curve 
of this interval in electric light. Ona glass plate I have ph 
f rectangular 
otographed the above 
curve of the major third passing through a set o codrdinates formed - 
«Lh £. 4 2. 7 1 * £, : an ana 
+ y 
equal parts. I now place this plate over the condensing-lens of a vertical lantern 
Ss. 
| is 
vered from the pipe, as th 
e swingi 
in the two planes of vibration, while the photographed curve on the lantern is pro- 
gressively covered with the sand if the tines of the two vibrations of the ‘ 
lum are to each other as 
Helmholtz, Tonempfindungen, 1857, p. 75. Crelle’s Jour. fir Math. Bad. lvii. 
, See Mach’s Optisch-Akustische Versuche, Prag., 1873, p. 91. Die Strobos- 
The Rev. S. B. Dod, one of the trustees of the Stevens Institute, has recently 
an experiment which neatly shows this. He silvered the tips of two me! 
deon reeds and then vibr planes at right angles to r, while a 
beam of light was reflected figure of their vibrations 
is the same as that obtained by two Lissajous’ forks placed in the same circull- 
a 
