336 
PHYSICS: C. BARUS 
The coil No. 10, with about 90 turns giving 0.001 volts per turn was 
substituted for B. With the ocular micrometer / obtained 10~^ ampere 
per scale-part. This is less than what was estimated; but a shortage is 
here inevitable. The fringes used were fairly large, but completely 
under control. 
Unlike the preceding case, the fringes now obtained were of the 
elliptic type, so that there is unison between interruptor and vibrator. 
The ellipses were often magnificent. There was little difficulty in meas- 
uring their breadth normal to the direction of fringes when quiet, as 
this is the fringe displacement. On making or breaking the circuit 
the ellipses oscillate in the well known way, and it may take a part of a 
minute or more before they subside into the bands (circuit broken). 
The ellipses remained in the field with resistances up to 10,000 ohms, 
below which the A N micrometer had to be adjusted to bring either axial 
extremity into view. Notwithstanding the feeble current, the tele- 
phone was still quite audible; so that the sensitiveness of the ear has 
not been exceeded. When the degree of resonance between the tele- 
phonic vibrator and the vibrating objective is exceptionally perfect, 
marked ellipses may appear in the absence of current, in spite of the 
fact that the telescope has an independent mounting. This very 
annoying phenomenon is hard to eliminate. 
Another smaller coil with but ten turns giving 0.001 volt per turn 
was installed with the object of ultimately approaching a condition of 
silence in an audible telephone. The results were striking throughout 
but can not be given here. 
7. Capacity and Selfinduction in the Secondary. — The phase differences 
thus far observed are attributable to the selfinduction of the secondary. 
It is interesting therefore to test whether the lead due to capacity can 
be equally well observed. The circuit, figure 2, was therefore pro- 
vided with a condensor C containing up to one microfarad, in 
steps of tenths. An auxiliary telephone T" was also inserted as a 
detector. The results were successful at once, as shown in figures 3 
and 5. In figure 3, = oo is the S3anmetrical eUipse, obtained on 
open circuit. This changed rapidly into the obUque ellipse C when 0.5 
microfarads were inserted, and the latter into the bands L (with a 
range of 30 scale-parts) when the circuit was closed with about 3000 
ohms. In another adjustment (fig. 5) of primary, R = oo gave nor- 
mal bands (i.e., the fringes do not vibrate); the capacity 0.5 microfarads 
now gave the oblique bands C and the selfinduction {R = 5000 ohms) 
the nearly symmetrical elHpse L. Space prevents the insertion of other 
relevant results. 
