48 
PHYSICS: C. BARUS 
Proc. N. A. S. 
and if this comprises X/2, the maximum energy will be ir/2 times larger. 
Thus the maximum work spent in compressing a cm. 3 , for n fringes between 
trough and crest, if p = 10 6 , X = 60 X 10 ~ 6 , p = 0.00129, I = 24 cm., 
R = 10 6 X 2.87, is 
irpC\ 
pAp/p 
2plR 
n = 10 3 X 13.7 n 
and the compression, Ap/p = 10 ~ 3 X 13.7 n. 
Observations with longitudinal pipes. — The open pipe, figure 1, was of 
9 
4 
2 
if 
u 
wood, with an inner cross-section 2.8 X 2.8 cm. 2 and length 24 cm. It 
responded perfectly to the fundamental, the softest producible note 
showing about 0.1 fringe in double amplitude, the loudest full note not 
more than a whole fringe. Blown so hard that the. note sharpened, the 
amplitude rather diminished. As in the case heretofore described, the 
mean energy lies between (I = 24 cm. here) 
pdp/p = 10 3 X 0.87 ergs/cm. 3 
and ten times this quantity. The maximum energy would, therefore, 
be 7r/2 times larger, which makes the energy content 10 4 X 1.37 ergs/cm. 3 
for the full note. 
The pipe did not at first admit of the production of the octave free 
from the fundamental. The wave pattern consisted of fundamental waves 
along the contours of which octave waves passed to and fro. The em- 
bouchure was, then, reset to give the clear shrill overtone alone. The 
waves now vanished evidencing complete symmetry in the dense and 
rare nodes present; proving, moreover, that the interferometer contributed 
nothing. 
Similar results were obtained with the closed pipe. The surprising 
feature of this closed pipe, however, was the occurrence of strong waves 
for the first overtone (fifth above octave). The two nodes, therefore, are 
here not symmetrically rare and compressed. The double amplitude of 
these waves for the very shrill note was 0.3 to 0.4 fringe. Neither the 
