164 PHYSICS: C. BARUS Proc. N. A. S. 
* 
The remarkable efficiency of glass quill tube probes, with the pin hole 
at a conical end, ground off, thus finds its explanation; for these are in 
conformity with s, figure 1. 
To further verify the new results, holes were bored with a fluted conical 
reamer in small discs of brass and these were then soldered to the ends of 
quarter inch-brass tubes, as shown at r and s in figure 2. The cones ended 
in pinholes, drilled from within and without, respectively, by fine needles. 
The case 5 gave positive deflections, r, negative deflections. It was found 
that on enlarging r from within with a needle, the deflections became 
positive; on further enlarging the pinhole, now from without, it became 
-20 0 20 40 -20 0 20 40 eO 80 iOO 
negative again. This proves, conformable with the earlier evidence, that 
only a very small depth of pinhole (probably of the thickness of a piece 
of paper) is effective and the remainder of the cone without importance. 
Fine slits cut in wax behaved similarly to the pinholes above mentioned, 
producing pressure for a salient wedge, and the reverse. The fringe 
deflections, 5, of figure 5, in which a resonator with a salient pinhole 
moves in y when tested with a reentrant pinhole resonator, supplied the 
results shown in figure 6. The maxima and minima are throughout 
negative. Both salient and reentrant pinholes function in the same way, 
with an inversion of sign, but without change of sign for the same pinhole. 
The question is thus adduced, as to whether the pinhole resonator with a 
reversed cone, figure 7, will also produce a reversal of fringe deflections. On 
trial an affirmative answer was obtained at once. As a rule the negative 
deflections are numerically smaller than the positive deflections. It was 
further found that the negative deflection decreases with the length of 
connector tube /, from the bottom of the resonator R to the reentrant pin- 
