Voi,. 7, 1921 
PHYSICS: C. BARUS 
211 
closed (resonator IV), or at least reduced to a shell-like space by a cy- 
lindrical inset, closed with a glass plate but a few millimeters above the 
mercury of the U-tube. 
A survey of the fringe displacement corresponding to different harmonics 
is given in figure 8, 1,000 ohms completing the telephone circuit. Their 
distribution is less regular than heretofore, and probably the smaller 
serrations have escaped detection. What particularly astonishes is the 
occurrence of resonance at the low notes, seeing that the resonator volume 
is here relatively negligible. The maximum displacement of 100 fringes 
corresponds to a pressure increment of about .03 cm. of mercury, which 
though twice as large as obtained with the large resonator III, is neverthe- 
less of the same order of values. 
In one respect the present curve (fig. 8) for the shell resonator IV, differs 
radically from the complete curve for the capacious resonator III. In the 
latter, conformally with the large volume, the lower notes (8-foot octave) 
are very much more effective than the notes of the one foot octave. The 
curve as a whole falls from left to right. In figure 8 the reverse tendency is 
observed. 
The question as to what resonates in case of the small resonator was 
approached by lengthening the tubing between the telephone and U-tube 
from its usual length of 48 cm., to 85 cm. and 120 cm. successively. The 
0 cm 4 8 1Z 
