46 A. M. Mayer on the Experimental Determination, ete. 
It will be observed that the accuracy of the determinations 
by this experimental method depend on three conditions. 
First, that the vibrating effects of the same area of a spherical 
sonorous waye diminish in intensity as the reciprocals of the 
squares of the distances of this area form the point of origin of 
the wave. There is every dynamic reason to believe in the 
truth of this proposition. The second necessary condition is 
that the elongation of one of the resonator tubes over the other 
by half a wave-length of firm glass tubing does not diminish 
the intensity of the impulses which have traversed it. Numer- 
ous experiments, especially those of Biot and Regnault on the 
aqueduct pipes of Paris, show that this short connecting tube of 
lass cannot in any way affect the accuracy of the measures. 
The third condition is that the intensities of pulses sent through 
a tube from a resonator vary directly with the intensities of 
precision the relative intensities of two sonorous vibrations pro- 
ducing the same note. 
Savart and many other experimenters have determined the 
relative intensities of two sounds by placing sand or other 
light particles on membranes and receding from the source of 
sound until no motions of the particles were visible. Also Drs. 
Renz and Wolf (Pogg. Ann., vol. elxxiv, p. 595) give the results 
of experiments on the determination with the ear of the inten- 
sity of the sounds of a ticking watch. More recently Dr. Heller 
(Pogg. Ann., vol. cexvii, p. 566) has made an elaborate research 
on the intensities of sounds; deducing mathematically his deter- 
minations from the observed amplitudes of vibration of a mem- 
brane; and Mr. Bosanquet (L. E. and D. Phil. Mag., Nov., 1872) 
has just published a paper in which he proposes to measure the 
intensities of the sounds of pipes of different pitch by the deter- 
mination of the quantity of air which each pipe consumes in 
sounding. But all of these experimenters acknowledge the 
want of precision in their measures and the difficulties in the 
actual practice of their methods. 
(To be concluded.) 
