50 ROYAL SOCIETY OF CANADA 
2. The velocity of the sound decreases as the intensity diminishes. 
3. The velocity approaches a limiting value, which is higher, the | 
greater the diameter of the tube. The mean value in dry air at 0° in 
a tube of diameter 1.00 m. is 330.6 m. 
4. The velocity is not affected by the mode of producing the — 
sound wave. 
5. The velocity in a gas is independent of the pressure. 
6. The ratio of the velocities in air and any other gas is V à 
where © is the density of the gas, supposed perfect. 
7. The average of the results of all the experiments in the open 
air 18/9290 0m rate 
tegnault was also the first to attempt direct experiments for deter- 
mining the velocity of musical sounds. In this case, however, the 
electric signals and the graphical recording apparatus were not sensi- 
tive enough to respond to the front of the wave, and it became neces- 
sary to resort to the ear alone. In these experiments Regnault had 
the co-operation of Koenig as observer, with whose assistance it was 
shown that : 
1. A note does not change sensibly when it traverses long distances. 
in tubes of large diameter. 
2. When the sounds are observed by the ear the velocity of high. 
notes appears to be less than that of low ones. This may be due to 
the more ready response which the tympanum makes in the case of 
low notes. 
3. In traversing tubes of great length, a note does not preserve its 
timbre, being resolved into its simple components. 
Regnault’s experiments have recently been repeated by M. Violle 
in the large sewers near Grenoble and Argenteuil, some of Regnault’s 
apparatus being employed for the purpose. The results of these experi- 
ments have not, however, been yet published. 
Diffraction—The phenomenon of the diffraction of sound was first, 
experimentally shown by Lord Rayleigh in 1880. } 
Pitch.—Before the last century, as already mentioned, Mersenne 
had attempted to determine the vibrations of a cord by deducing them, 
from very slow vibrations of the same cord when lengthened. Chladnvs 
tonometer, which consisted of a vibrating metal rod of variable length, 
was based on the same principle. In 1819 Cagniard de la Tour invented 
the siren, a much superior instrument, but incapable of giving very exact 
results, notwithstanding the simplicity of its mechanism. The same 
remark may be made of the toothed wheel invented by Savart in 1830. 

