Vol. 7, 1921 
PHYSICS: C. BARUS 
209 
size of resonators, whether the region be closed, open or partially open. 
Conical Vents Reversible. Periodicity. — The conical vents c' (fig. 1) may- 
be inserted into the branch tube t" in two ways, either in the salient posi- 
tion a with the convex surface around the pinhole 0 outward (fig 3) ; or 
in the reentrant position (fig. 4) with the convex surface at 0 inward. The 
results obtained are usually reversals of each other, so that a pressure 
excess is liable to be on the concave side of the conical vent. These re- 
sults were always consistent in character; but it was soon found that the 
strength of the telephone current and the length I of the tube c'c' in the 
reentrant position (fig. 4) greatly modified them. When there is no re- 
sistance in circuit, i.e., when the telephone sounds harshly, reversal ceases, 
so that either the case 3 or 4 produces a pressure within ; but even here, on 
closing the circuit, the fringes in case 4 are seen to move first toward a 
dilatation and then turn in the direction of pressure. 
The position (fig. 3) being the normal case investigated above, the case 
4 was studied with 1,000 ohms in circuit, and for different lengths I of the 
quill tube c' y beyond O, from I = 2 to over 40 cm. These results are 
given (fig. 5) the abscissas showing the length / of tube taken and the 
ordinates the fringe displacements s, both for the region R' alone (positive 
displacements here denoting dilatation) and for the region R (positive 
displacements denoting pressure). The results are periodic in marked 
degree, so that the quill tube (fig. 4) is a musical instrument with a pinhole 
embouchure; and in fact while the case 3 is nearly silent, 4 audibly re- 
produces the sound of the telephone. The curve for R' shows two reso- 
