Vol.. 8, 1922 
PHYSICS: C. BARUS 
327 
Similarly in case of binaural telephones, one corresponding to each 
shank of the U-tube, Sq = 152, ro = 49,500, the results were, for example, 
r X 10-3 14 23 33 43 ohms 
^ observed 105 65 41 25 fringes 
s computed 103 66 41 25 fringes 
If the effective voltage is constant and 5 = 1 in the equation, r' = 
To log So, where is the resistance needed to reduce the deflection to one 
fringe. Hence r ' is an index of the sensitiveness of telephones, all operat- 
ing in the given circuit successively. A number of tests so made ranged 
from f' = 3 X 10^ for common telephones to = 10^ for high resis- 
tance telephones. 
The meaning of the equation given is not so easily determined, since 
the acoustic pressure is produced through the intermediation of the tele- 
phone mechanism. If we suppose that, within limits, the amplitude a 
of the air waves produced at the plate is proportional to the amplitude 
of the current in the telephone, the exponential equation would then 
belong to the acoustic pressure p, and may be written, p = poe^°^^. This 
seems to me probable, as it would explain the absence of registry in case 
of the pinhole resonator, for instance, when the sounding organ pipe is 
over 5 meters distant; i.e., the rapid decline of the fringe deflection with 
the distance of the source of sound may thus be quantitatively evaluated. 
* Advance note from a report to the Carnegie Institution of Washington, D. C. 
THE EQUILIBRIUM POSITIONS OF THE VACUUM GRAVITA- 
TION NEEDLE IN iq2i AND 
By CarIv Barus 
Department of Physics, Brown University 
Communicated, September 20, 1922 
The apparatus used last year was identical with the present one, ex- 
cepting only the minor appurtenances, added to secure greater conve- 
nience in exhaustion. These are without influence. Moreover neither 
the location of the apparatus nor the mechanism of the weights M had 
been changed. The method of observation was substantially the same. 
It is thus very difficult to account for the erratic behavior of the gravita- 
tion needle during July and August of this year, as compared with the 
nearly constant deflections (A3;, y being the telescopic scale reading in 
centimeters) obtained under like conditions last year. I have, therefore, 
in the figure, put the static elongations y for the same day in 1921 and 
