that experiment, consistently with the theory, proves that the speed
increases with the amplitude, or, if you will, with the intensity. M.
Violle has published an important series of experiments on the speed
of propagation of very condensed waves, on the deformations of these
waves, and on the relations of the speed and the pressure, which
verify in a remarkable manner the results foreshadowed by the already
old calculations of Riemann, repeated later by Hugoniot. If, on the
contrary, the amplitude is sufficiently small, there exists a speed
limit which is the same in a large pipe and in free air. By some
beautiful experiments, MM. Violle and Vautier have clearly shown that
any disturbance in the air melts somewhat quickly into a single wave
of given form, which is propagated to a distance, while gradually
becoming weaker and showing a constant speed which differs little in
dry air at 0° C. from 331.36 metres per second. In a narrow pipe the
influence of the walls makes itself felt and produces various effects,
in particular a kind of dispersion in space of the harmonics of the
sound. This phenomenon, according to M. Brillouin, is perfectly
explicable by a theory similar to the theory of gratings.




CHAPTER III

PRINCIPLES


§ 1. THE PRINCIPLES OF PHYSICS

Facts conscientiously observed lead by induction to the enunciation of