Vol. 7, 1921 
PHYSICS: C. BARUS 
49 
waves nor the sound gave any indication of the fundamental. Thus 
the node at the closed end of the pipe is a semi-node 5, figure 2, while 
that nearer the open end is a full node 55, and the difference found 
is equivalent to the mean energy of the former and should be trebled. 
The duodecimal overtone was also obtained sharply. 
Finally the temperature equivalent of the mechanical energy per fringe, 
computed either as JcpAt = pAp/p, or as At = r{k/c— l)Ap/p comes 
out 1.5° C, if r = 273°. Some years ago I tried to measure this with 
a bolometer-telephone device, but failed. This reason seems to be that 
in case of these rapid alternations, heat does not enter the wires appreci- 
ably. 
Reed Pipes. Voice. — In the endeavor to obtain waves of larger ampli- 
tude, the device resorted to was a brass pipe 32 cm. long and 3 cm. in 
diameter, through which the component ray of the interferometer passed, 
provided with a tubulure about 1 cm. in diameter at its middle. This was 
then connected with flexible tubing to the reed box. The note was coarse 
like a bassoon. 
With the flexible connector very short, the first experiments gave a 
display of enormous waves, 20 or 30 fringes high. I suspected that this 
could only be a direct mechanical effect of the sonorous reed on the inter- 
ferometer. The reed pipe was, therefore, mounted on a separate scaffold- 
ing, entirely independent of the interferometer. The result was an im- 
mediate reduction of double amplitudes to a few fringes. On replacing the 
reed by an clarionette mouth piece, the results were similar. 
The pipe was now moved, as a whole, out of the range of the rays of 
the interferometer and sounded. To my astonishment, strong waves 
were again produced, nearly as much so as when the pipe was in position 
for interference. In other words, these reed notes act directly on certain 
parts of the interferometer, and excite the parts selected by resonance. 
To test this further, I made use of the voice, singing a foot or more 
away from the interferometer. At certain chest notes (b, c') t the fringe 
bands broke into marked waves near a fringe in double amplitude, the 
effect being absent from the remainder of the scale. A clarionette played 
about a yard or more from the interferometer evoked the following response : 
e..g a b c' d' e f f g' a'..f 
0 . . 0 strong stronger Max. strong weak 0 weak no response 
1.2 fringes 
Resonating pipes on the interferometer had no discernible effect. The 
seat of receptivity is probably the iron base of the apparatus. Loading 
it depressed the maximum to b. A totally different interferometer, in 
a new location, showed the same behavior on the same base (lathe bed). 
In a third interferometer of different construction and on a different base, 
the clarionette e was most effective, b, c', /', a' marked the remaining 
