338 
PHYSICS: C. BARUS 
suppose. The effect moreover is particularly marked if the telephone 
is open, i.e. with no connection between the clamps. The stray vibrat- 
ing field produced by a small electromagnet (say J inch iron, 2 inches 
long) is thus quite audible even beyond 50 cm. from the electromagnet. 
The degree of response depends moreover on the orientation (fig. 6) 
of the telephone relative to the electromagnet E. If we take the three 
cardinal positions of the plane of the coil or the diaphragm, the vertical 
positions d, /, and the fore and aft horizontal positions h, g, i, have 
their maximum response in the plane of symmetry gd E. The right and 
left horizontal positions d'\ b, a, c, d\ give minimum response (tele- 
phone silent) in this plane (E, a), with maxima at symmetrical positions, 
b and c. A convenient reversal of magnetic field is thus obtained. 
Although all telephones show the phenomenon pretty well, since it is 
more distinct on open circuit (which implies a current oscillating from 
damp to clamp) it would be well worth while to wind a telephonic 
bobbin provided with a capacity for the particular purpose of catching 
the stray magnetic field, such as is here encountered. Without pro- 
ceeding to this extent, I used the telephone as a secondary as shown in 
figure 7, where E is the electromagnet of the interruptor /, 5 being the 
vibrating break circuit spring. The telephone depending adjustably 
from the sleeve a may be slid right and left or rotated into any hori- 
zontal position relative to E, and the current obtained measured by the 
vibrator. 
In the endeavor to minimize the mechanical coupling, the telescope 
(separately mounted) was placed at about a meter from the vibrator. 
In this case the phase difference of the vibrations of fringes and objective 
was annulled, but the bands in the absence of current were nevertheless 
somewhat oblique to the direction of the vibration of the objective, 
showing that the fringes still vibrated. 
With this exception the behavior of the telephone inductor was ad- 
mirable. In passing from the positions 6 to c by sliding the telephone, 
the ellipses regularly passed through the oblique bands, indicating that 
these successive ellipses, even if of nearly equal size, were opposite in 
their phase rotation. This was the case when the secondary was closed 
with 5000 ohms and the inevitable inductance; also when a capacity 
was placed in the secondary and finally on passing from an inductance 
to a capacity in the secondary. The effect produced by changes of 
capacity of 0.5 microfarad was marked. The alternate-current effect, 
moreover, was still apparent when the circuit was closed with 25,000 
ohms and the telephone practically silent. 
