210 
PHYSICS: C. BARUS 
Proc. N. A. S. 
nance maxima and one minimum, but in all cases the dilatation (positive- 
displacement s) within R' is sustained, merely changing in degree. The 
curve for R, however (dilatations for negative s) indicates the occur- 
rence of both dilatations and pressures within this (smaller) region. Both 
curves are quite consistent (although R' is nearly four times more capa- 
cious than R) and one may infer the length of pipe Z = 30 cm. (fig. 5) or the 
wave length 21 = 60 cm. to be an harmonic of the telephone interruptor. 
This was in fact close to the four foot c. 
In a majority of cases the action of the conical vent thus recalls the 
behavior of the cup anemometer, as the pressure excess is on the concave 
side; but the lower curve of figure 5 (for R smaller) is out of keeping with 
this, as between lengths of 20 and 35 cm. of pipe, the pressure excess is 
within, or on the salient side. 
Resonators of Very Large Capacity . — The volume of the region R' (fig. 1) 
was now further increased by adding an additional cylindrical tube 6.2 cm. 
in diameter and 10.7 cm. high, closed on top with a glass plate. All parts 
were (as before) carefully cemented together. The volume added was thus 
370 cm. 3 , as compared with the original 48 cm. 3 , the ratio of volume in- 
crement being 6.7, and the ratio of total to original volume 7.7 The coni- 
cal vent c', figure 1, here acted much better than the copper foil pinholes c. 
Using the motor break and conical valve, the fringe displacements were 
observed for frequencies between the notes g' and c'" and both with 1,000 
ohms and 500 ohms in the telephone circuit. An example of the results 
is given in the two curves in figure 6, the region R being in communication 
with the atmosphere and R' closed except as to the salient conical vent 
specified. The curves are remarkable because of the sharpness of the 
maxima, which are apparently overtones in the key of B or B flat. It is 
obvious that the fundamentals of the large closed reservoir R' will lie very 
low as compared with the frequencies of the diagram and very large fringe 
displacements may be looked for and were found there. The height of 
the maxima gradually decreased from g to c"' there. 
It was now thought desirable to test the conical vent in the reentrant 
position and data of this kind are given by the curve in figure 7. All the 
maxima are here dilatations, laid off positively for convenience in com- 
parison with figure 6. The valve action (500 ohms in circuit) is much 
weaker in figure 7 than in figure 6; but in every other respect figure 6 is 
symmetrically reproduced. This is a very disconcerting result; for it is 
not the impulsive displacement of the telephone plate alone which pro- 
duces the pressure increments within, even if a reversal of the telephonic 
current (change of poles) changes pressure increments into pressure de- 
crements. The reversal conical pinhole vent in association with a given 
adjustment of telephone current (poles not changed) will do the same. 
Resonator of Very Small Capacity. — Finally the resonator R r was all but 
