Daily Republican., 1881-08-06
A Description Of Bell's Induction
Balance.

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EXECUTIVE MANSION, Washington
ID. g., Aug. 1.-The induction balanc
used by Professors Bell and Taintor ii
the experiment made this morning fo
the purpose of ascertaining the location
OF the ball in the Presidents body differ.
very materially from the apparatus
with which they began experimenting
several weeks ago Important modifi
cations aud changes have been made in
the shape, size and arrangement OF the
induction coils; the small clock, which
was a part of the original apparatus
has been dispensed with, and conden.
ser has been introduced into the PR
mary circuit.
The result of those notifications and
improvements is an apparatus which,
although not essentially new in princi
ple,i more sensitive to small masses OF
metal at distance, and better adapted
to the requirements of military surgery
than anything of the kind hitherto do
vised. the apparatus, in its present
improved fora consists 1f two flat coils
about four inches in diameter and one
half an inch in tt icknrss of insulated
copper wire, battery, a condenser, an
interrupter or circuit breaker, and a
telephone. The ends of the primary or
inducing coil are connected with the
poles of the battery, and in the same
circuit are Il condenser and small in.
terrupter, whose vibrating tongue opens
and closes the circuit with great rapdi-
ty. The ends of the secondary coil, in
which the current is to be induced, are
carried to the binding posts of the Bell
telephone. When the c INJECTIONS have
thus all been made, the secondary coil
il laid on the primary or inducing coil
so that taeir respective cilcumfprences
exactly coincide. The circuit breaker
is then set IN motion, aud the rapid v
interrupted current of higher intensity
in the secondary coil, and, rs it does o,
a loud musical tone is heard in The tel
ephone with which the secondary coil
is connected. As long as tho current is
maintained and thu circumfnren"e of
the two coils are kept in exact coinci-
dencr, the musical note in the telephone
does not change its pitch or Intensity.
If, however, the experimental slides
TIE upper COIL along an inch ,r so upon
the corner 30 that tn.ir circumterenceS
no longer correspond the intensity of
the musica t0ue is diminished, and
Just in proportion as the centres of the
fiat calls are separated by IA greater or
less distance the Intensity of he musi-
cal tone is lpssened OF increased. When
the upper coil has been sli,idcn over The
lower so that they simply oTerlap the
centre of one CORRESPONDING nearly with
u point on the circumference in the
other, the musical tone in the telephone
ceases. 1t the upper coil be pushed ii
little further to oae side, so that it over.
laps still less, The tone is again heard.
BY delicate manipulation 1t is possible
TO adjns the centres OF the Overlapping
coils at such a distance, one from the
other. that IL perfect balauce is brought
about, and, when this is the case, the
telephone makes no sound whatever.
The centres of the overlapping coils
cannot then be moved either towards or
away from one another without caus-
ing the telephone to break its silence.
When the coils are thus balanced and
the telephone is mute. IL is found that
what may be called the area Of coinci
dencc, or, in other words, the area of
the overlapping parts of the two fiat
coils has become highly sensitive to
the approach of metal, and manifests
lis sensetivness by a low note in the
telephone. AS long as metal IL kept
away from this area the telephone re-
mains silent, but, if IA piece Of lead, for
example, is brought within distance
Of four or Ave inc' es from the overlan-
ping part, Of the coil, there may be
heard in the telephone a FAINT but clear
ly prectplible note which heco,ues loud
er and louder a, the metal approaches
the sensitive surface, and throws the
coil more and more out VI balance. 1t
will readily be seen that under the
guidance If the telephone, the small
area bounded by the inte1sectinC cir
conferences If the overlapping coils,
can DC placed exactly above bullet or
other piece of metal embedded in the
body, provided the metal does not lie at
too great depth.
AS soon as the balanced coils begin to
feel the disturbance caused by the
deeply embedded bullet, the telephone
announces the fact by IL faint, contin-
uouS musical note, and 1niS note grows
louder and londer until the overlapping
parts OF the coil are directly above the
the disturbing metal, when the sound
reaches its maximum. For convent
'ence of application tr the body the coils
used by Professor Bell this morning,
were mounted in rectangular piece Of
walnut, about seven iuL he, in length by
four in breadth, with screw posts at the
corners for the wires and a handle at the
back by which it could be held.