82 PHYSICS. 
which expresses its specific heat under a constant volume. The value of & 
for atmospheric air has been found to be 1.421, hence /k = 1.192, and 
substituting the various values in the above formula, it becomes 
v = 916 X 1.192 (1 + .00104¢) = 1092 +. 1.14¢, where ¢ is the number of 
degrees above 32° F. The velocity of sound in the air is therefore 
dependent upon the temperature, and not upon the pressure of the atmo- 
sphere. From this formula the velocity of sound in other gases may be 
determined. whenever the value of k is known, or k may be determined 
from the known velocity. 
Since sound depends upon condensations and rarefactions, and such 
media alone can propagate it as are capable of this, it follows that this 
velocity of sound in fluids depends upon their compressibility. This com- 
pressibility must be obtained by direct measurement, for which purpose 
Oersted invented the Piezometer. By the use of this instrument and 
calculation, it has been found that in water of 54° F., the velocity of sound in 
a second amounts to 4630 feet; direct experiments by Colladon, in the 
Lake of Geneva, have given results indicating a velocity inferior to the 
above by less than sixty feet. 
The same principle holds good in general for solid bodies. Chladni and 
Savart have instituted very extended experiments on this subject, and have 
found that this velocity is universally greater than in the air, being least, 
however, in whalebone, where it amounts to 62 times, and greatest in deal, 
where it is 18 times greater than that in the air. 
If several solid bodies be united together, sound is transmitted with great 
facility throughout the whole mass, and, arrived at the extremity, the sound 
waves partly pass into the contiguous medium, whether fluid or gaseous ; 
they are, however, partly reflected, and form their standing vibrations with 
the re-entering waves. If, however, the whole system of bodies is set into 
vibration simultaneously with each individual point, they lose their indivi- 
dual character in a great measure by this union. Upon this circumstance, 
among others, depends the variety of musical instruments, and this is the 
reason why, for example, two equally proportioned pianos may exhibit a very 
different character with respect to sound and tone. 
Although vibrations are readily transmitted over a system of uniform 
bodies, solids for instance, this takes place with more difficulty when the 
bodies are different, as from solids to fluids or gases. Here the vibrations 
of the sounding body must be communicated to another, for the purpose of 
being increased in intensity: in other words, its vibrations are strengthened 
by resonance. An example has already been given of the strengthening of 
sound by a tube; another is to be found in the sounding board, where the 
vibrating strings are brought into contact with a large thin surface easily 
set into vibration. 
In a similar manner bodies may be set into vibration by a sound wave in 
the air, as a door, a window, and even strings themselves. Here the sound 
waves in the air, started by the vibrations of a solid body, or even the ori- 
ginal vibration of the air itself, come in contact with the body,causing it to 
vibrate in concert. Savart has ocularly demonstrated such sympathetic 
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